Seperate application layer interpretation and storage model scheme.

[greymistcube]

As I have mentioned in #3570, IAccount still has too many responsibilities. This is due to many reasons, one of which is having application layer logic seeping into IAccount interface. I suggest having a middle layer such as IRawAccount to separate the two. We can try to extract Currency/FungibleAssetValue handling altogether by removing Mint()/Burn()/Transfer() from IAccount, but I think this can come later after the layers are separated (and would be actually rather hard as everything is so strongly coupled). I'd also note that cost of maintenance anything related to IAccount is exceptionally high due to lack of pure libplanet side model.