Portfolio value of a user

[bvotteler]

Add portfolio values tracking per user for all assets ~converted to BTC and/or USDT~.

~Note: Some assets may not have oracle values (to get BTC value). Meaning we need to rely on other sources to get an exchange rate.~

Update: Removing conversion requirement. To be done at a later stage, possibly not as part of squid processing.

[bvotteler]

We should be able to keep tally of a regular (ie. not modl, fees type) account's balance by tracking 4 events:

• tokens.withdrawn
• tokens.deposited, and
• tokens.transfer
• tokens.slashed