[Refactor] BaseConnection method extraction

[tuliomir]

On #533 there was a discussion on inheriting too many methods that are only useful for fullnode Websocket connections when connecting to other kinds of servers ( ex.: Atomic Swap Service )

It would be a good idea to refactor these fullnode-specific methods into a new core-connection file. This would imply on also refactoring the wallet-service websocket, that already inherits these unnecessary methods.

The concept of the BaseConnection itself would be re-evaluated.