Move bot functionalities (called Gossip) to a separate source file
gossip: add methods "SendMessage", "JoinChannel" and "LeaveChannel"

Each command had to implement the IRC commands themselve and was
just using Gossip's connection. Add methods for usual actions to
Gossip so that commands can just use them.
Merge pull request #11 from ralfth/enhance-gossip

refactor(gossip): restructure project

Move IRC specific functionality to separate source file. And avoid duplications by extracting methods. (thx to ralfth)