Moved callback execution to separate methods.

[deepadmax]

I've moved the execution loops of callbacks to separate methods. This is so that the behaviour can be containedly redefined without needing to hard-rewrite all surrounding logic. As it is now, subclassing the client and adding functionality on running the callbacks would entail needing to keep an eye out for any changes to these whole methods upstream, lest an update be missed and either break it or simply not benefit from patches or upgrades to the flow.

[PaarthShah]

Looks like the unit tests weren't too happy with it, but I really do like this concept and I think it's absolutely a move in the right direction