Transfer fee improvements/reduction

[gordsport]

TODO:

• Only charge transfer fees if not offset by last epoch fees paid/generated by sender [for first N transfers?]?

We need to update the spec to detail that for each party cumulate the fees paid over an epoch, store the value if there is a transfer subtract the fee from the stored value. When this hits zero party gets charged. Need API support so front end can make it clear how much is transferred for free.

Done:

• Cap transfer fees for larger transfers (multiple of the minimum amount) (in feat: add a cap for transfer fee)