[feat] Custom key:value pair to transaction/payment

[AnimusXCASH]

Allow for creation of one custom key value pair to the transaction. It would be owned by account/transaction with key being a string and value 32 bytes. The fee for transaction would be increased as per key value pair size.

This would allow developers and businesses integrating xcash chain to structure activities around meta data attached at the application layer. They would specify what key values mean and make further processing.