Merge signature scheme of value transfers (#287)

* Refactor: cleaned up unused files

* Refactor: changing branches (need to commit)

* Refactor: refactored some code

* Feat: finished signature scheme for value transactions

* Fix: fix broken merge

* Refactor: refactored some code

* Refactor: refactored transaction marshaling and unmarshaling

* Fix: fixed missing err check

* Feat: added payload string method

* Feat: added Bytes() method to transactionid