## Transaction multi payment
### Overview
This noble provides functionality to accepted transaction fees in other currencies. Extends substrate's `transaction-payment` pallet.
### Interface
Extends `transaction-payment` interface to add functionality to set desired currency and to add members who can add or remove accepted currencies. - `set_currency` - set selected currency 
in whci all transactions fees will be paid. Balance of selected currency must be non-zero. - `add_member` - only root can perform this action - `remove_member` - only root can perform this 
action
### Implementation details
Transaction fees are paid in native currency by default. This pallet allows to set a different currency to pay fees with for an account. When the transaction fees is being paid and chosen 
currency is not native currency - swap is executed to obtain fee amount in native currency first. The swap (or buy) is done via selected AMM pool. Subsequently, the fee is paid in native 
currency.