Implement MintCoins method that matches x/bank MintCoins validation behavior
- Validate total fractional amounts in genesis type - Validate against fractional balances such that `(sum(balances) + remainder) % conversionFactor == 0` - Add new utility type `SplitBalance` for splitting up full balances into each
- Add initial setup and empty genesis type for x/precisebank - Basic tests with mostly empty values, to be filled out with additional implementation
