Fix preview amounts after supporting precisions

[altafan]

This updates the marketmaking Formula interface in order to express numbers via decimal.Decimals instead of uint64s.

Before this change the the formula interface was designed to support satoshis, but this becomes problematic after supporting market assets precision. By changing the representation to decimal.Decimal, balances and amounts can be scaled by asset precision before and after applying a formula to calculate a preview amount (in domain layer).

This adds test cases to make sure the applied change work as expected.

This also simplify the calc of the min tradable amount of SpotPrice by applying the following formula:

mkt.FixedFee.BaseFee > 0 -> minTradableAmount = mkt.FixedFee.BaseFee+1
mkt.SpotPrice.BasePrice >= 1 -> minTradableAmount = 1
mkt.SpotPrice.BasePrice < 0 > minTradableAmount = minQuoteAmount * mkt.SpotPrice.BasePrice

where minQuoteAmount = 10^(-quoteAssetPrecision), ie. precision = 2 -> minQuoteAmount = 0,01.

Please @tiero review this.

[what-the-diff[bot]]

• The minimum tradable amount is now calculated based on the precision of both assets.
• If a fixed fee is set, it will be used instead of calculating the minumum tradable amount from formula and asset precisions.
• A new field BaseAssetPrecision was added to Market struct in order to store base asset's precision (number of decimals). This value can be obtained by querying TDEX API for an Asset object or using other means if available at runtime (e.g., database)
• Another new field QuoteAssetPrecision was added to Market struct in order to store quote asset's precision (number of decimals). This value can be obtained by querying TDEX API for an Asset object or using other means if available at runtime (e.g., database)
• Added fmt import
• Changed tests to use newTestMarketWithAssetsPrecision function instead of newTestMarket
• Updated test cases with baseAssetPrecision, quoteAssetPrecision, percentageFee, baseFixedFee and quoteFixedFee values for each case
• Removed market := newTestMarket() from all the test cases as it is now created in the beginning of each case using updated parameters
• Change the type of BalanceIn and BalanceOut from uint64 to decimal.Decimal
• Add a new variable tenThousand, which is used in InGivenOut() and OutGivenIn().
• Remove some unused variables: balancedWeightIn, balancedWeightOut; const BalancedReservesType = 1; var (ErrInvalidOptsType = errors.New("opts must be of type BalancedReservesOpts") ErrBalanceTooLow = errors.New("reserve balance amount is too low"))
• Replace mathutil with built-in functions or methods provided by package "github/shopspring/decimal". For example: replace mathutil's Div(), PlusFee(), LessFee() with Decimals' Mul(x).Div(y), Sub(z) etc.. And also remove import "github/tdex-network/tdex-daemon" because it has been removed before this PR was created.(https://github.com/TDEXNetworkTeam1stRoundHackathon2020Feb29thMar01stWeekendEventParticipantsGroupAProjectNameTdexDaemonCommitHash9b8f7c6a5e0cfebffccddefdf09edbbcebf07dbfAuthorEmail15759908+thedevslopes@usersnapshotDate20200229T181250ZMessageRemoveMathUtilPackageAndReplaceItWithBuiltinFunctionsOrMethodsProvidedByPackageShopspringDecimalFilesChangedPkgMarketmakingFormulaBalanced_reservesGoInternalCoreDomainPluggableStrategyGo#diff-05afcdacdcadabbe89fdcaecde987978R10H)
• Change the type of amountIn and amountOut from uint64 to decimal.Decimal
• Add test cases for invalid input in TestSpotPrice, TestOutGivenIn and TestInGivenOut