Implement unit_of_account Pallet

[dharjeezy]

We need to implement a new pallet. This pallet draws inspiration from this totem doc

STORAGE

• This pallet will introduce a storage called CurrencyBasket which can be a StorageMap of a particular currency to it's issuance which is a LedgerBalance and the weight(w) that will be calculated.

• This pallet will also introduce another storage called Neer(Nominal Effective Exchange Rate) which is the actual Unit of Account and which will be a StorageValue

• This pallet will also introduce another storage for whitelisted accounts that are allowed to send extrinsics to update the basket of currencies maintained

EXTRINSICS

• This pallet will introduce an extrinsic for adding whitelisted account

• This pallet will introduce an extrinsic for removing whitelisted account

• This pallet will introduce an extrinsic for adding a new Currency to the CurrencyBasket storage. When a new Currency is added to the basket/pool, we calculate the weight(w) for that currency and also re-calculate and update the Neer(Nominal Effective Exchange Rate) for the pallet, as this will change.

• This pallet will introduce an extrinsic for removing a Currency from the CurrencyBasket storage. When a Currency is removed from the basket/pool, we re-calculate and update the Neer(Nominal Effective Exchange Rate) for the pallet, as this will change.

TODOS

• [x] Add related storages as explained
• [x] Add related extrinsics as explained
• [x] Write Tests
• [ ] Benchmark Extrinsics

[chrisdcosta]

Here is a table of test data:

Before the inverse issuance is calculated, the number of decimals should be added to the Total Issuance. This aligns each currency appropriately to the smallest currency unit according to the number of decimal places.

We cannot check that the total issuance is appropriately supplied by an extrinsic, but we can use the number of decimals as a crude sanity check: that the supplied value is within a certain expected range +/- the existing value.

Weighting per currency = Inverse Issuance / Total Inverse Issuance
Weight adjusted price = Weighting per currency * Price
Unit of Account per currency unit = Price / (100_000 * Unit of Account)

Symbol	Decimals	Total Issuance	Inverse Issuance	Weighting per currency	Price	Weight adjusted price (for Unit of Account calc only)	Unit of Account per currency unit
CNY	2	20308000000000000	0.00000000000000004924	0.000693859246235965	$0.14	0.0000978362008771359	0.00000261216547787
USD	2	1564692617100000	0.00000000000000063910	0.009005534645313300	$1.00	0.0090055346453133000	0.00001852560865275
EUR	2	1214125230000000	0.00000000000000082364	0.011605799158427800	$1.08	0.0125213275644432000	0.00001998700917578
JPY	2	138166400000000000	0.00000000000000000724	0.000101984951280195	$0.01	0.0000009335163936936	0.00000016957363967
GBP	2	288957500000000	0.00000000000000346072	0.048764588469100100	$1.23	0.0599569675118472000	0.00002277758002272
KRW	2	414795400000000000	0.00000000000000000241	0.000033970708384326	$0.00	0.0000000276252556365	0.00000001506517524
INR	2	16370023000000000	0.00000000000000006109	0.000860774207376494	$0.01	0.0000113059188514640	0.00000024332632914
HKD	2	1481642700000000	0.00000000000000067493	0.009510318224872960	$0.13	0.0012266664811812900	0.00000238948294268
CAD	2	262358300000000	0.00000000000000381158	0.053708586968889400	$0.71	0.0379834314115889000	0.00001310155834163
TWD	2	4661099100000000	0.00000000000000021454	0.003023083884348220	$0.03	0.0000999863125741122	0.00000061272110475
AUD	2	216420000000000	0.00000000000000462065	0.065109017524073500	$0.61	0.0394104957988599000	0.00001121355304909
BRL	2	674888154000000	0.00000000000000148173	0.020878857465558600	$0.19	0.0039026380942576900	0.00000346277310273
CHF	2	107432400000000	0.00000000000000930818	0.131160558384249000	$1.02	0.1340108806726950000	0.00001892819885136
RUB	2	5062290000000000	0.00000000000000019754	0.002783501848483590	$0.01	0.0000364605586142105	0.00000024266340635
THB	2	2086203000000000	0.00000000000000047934	0.006754325237074240	$0.03	0.0002054292610286960	0.00000056344667484
SAR	2	194879800000000	0.00000000000000513137	0.072305562570158500	$0.27	0.0192247009959278000	0.00000492561394251
AED	2	169370000000000	0.00000000000000590423	0.083195923555293000	$0.27	0.0226502222965908000	0.00000504362637294
SGD	2	65602100000000	0.00000000000001524341	0.214793330892761000	$0.70	0.1496416541090850000	0.00001290637242159
MYR	2	196142970000000	0.00000000000000509832	0.071839911328761800	$0.23	0.0164437464095326000	0.00000424040627464
MXN	2	1075609856600000	0.00000000000000092971	0.013100376020261900	$0.04	0.0005215518782401990	0.00000073754111893
TRY	2	266853972700000	0.00000000000000374737	0.052803761660318700	$0.15	0.0077898346674402500	0.00000273297628769
VND	2	921184805000000000	0.00000000000000000109	0.000015296489364650	$0.00	0.0000000006472876744	0.00000000078393139
SEK	2	375795200000000	0.00000000000000266102	0.037496204242523500	$0.10	0.0036834625288696500	0.00000181987448264
PLN	2	155778160000000	0.00000000000000641939	0.090454872316889500	$0.24	0.0213682357059139000	0.00000437632116599
			Total Inverse Issuance			Unit of account (sum of all)
			0.00000000000007096782			0.5397933308126700000

[chrisdcosta]

The storage should contain:

• Symbol (up to 7 alpha numeric)
• Total Issuance
• Price
• Unit of Account per Currency Unit

In other storage store the Unit of Account as a simple value that gets overwritten each time it changes.

Since we normally use Ledger Balance which is u64 the floats should be converted for storage by multiplying by 1_000_000_000_000_000_000. There are conversion utilities in the primitives directory.

The weighting per currency changes for all currencies, whenever at least one issuance changes. This also implies that Weight adjusted price and Unit of Account per currency unit changes for all currencies even if the price is not updated when an issuance change happens.

Additionally Weight adjusted price and Unit of Account per currency unit must also be updated when the price changes.