Refactor transaction related code

[AnthonyLaw]

You can see that many common files need to be touched when adding a new transaction. Examples are CreateTransaction.js, TransactionService.js, etc.

It could be possible to have a TransactionTypeHandler interface and a TransactionTypeManager object that controls instances of the interface.

The manager selects the right handler by transaction type (and probably version) and delegates the different methods. Then, adding a new transaction type is just creating a new implementation of TransactionTypeHandler and registering it to the TransactionTypeManager.

I move your comment here, in case i forget :)

CC: @fboucquez