AIP #61 v5: Unified precision (8)

[elpiel]

https://github.com/AdExNetwork/aips/issues/61

Create a Unified Precision number (UnifiedNum) with precision of 8 that will be used for all calculations, except when we are creating the MerkleTree, where we need the actual precision of the token in order of the MerkleTree to be calculated properly.

• (PR Adapter calculate and retrieve total spendable amount #385) Token configuration of actual precision (in the configuration of the whitelisted token addresses)
• Use Unified Precision - UnifiedNum (including DB) & floor all the calculations
• Postgres type: bigint
• (PR AIP#61 AdEx V5: Targeting rules use UnifiedNum #412) Targeting rules DSL - use UnifiedNum instead of BigNum (see V5 Targeting DSL - UnifiedNumber instead of BigNumber adex-protocol#67)

[elpiel]

Postgres: Since we are using a u64 to store the UnifiedNum we can use bigint (max of 9_223_372_036_854_775_807) and although we can handle half of what u64::MAX = 184_467_440_737.09551615, it should not cause any issues.
Otherwise an error will be raised by the database and caught in Sentry.