* add decimals parameter to unitsToAmount() and amountToUnits()
* unify use of amountToUnits() and unitsToAmount()
* use tokenDecimals in TokenUtils
* add tokenDecimals to functions in SideStaking
* add parameters to doc comments
* calculate amountToUnits and unitsToAmount using decimals in FixedRateExchange
* remove unused amountToUnits() function from SideStaking
* use decimals in unitsToAmount() function in Pool
* add tokenInDecimals and tokenOutDecimals to TokenInOutMarket interface
* use decimals in amountToUnits() function in Pool
* fix errors related to pool decimals
Co-authored-by: mihaisc <mihai.scarlat@smartcontrol.ro>