Enhancement: Make log types pluggable

[cjthompson]

Currently the list of log modules is hard coded in bucker. It would be nice to provide a plugin mechanism to register additional modules.

For example, if I want a customized logStash module, I could just write my own and register it without having to fork the repo.

[nlf]

This is a goal for the refactor that I'm working on, so I'm going to leave this open as a reminder