Deleting unneeded config file
Add class-level #tracked_field? and #tracked_fields methods; refactor logic to determine whether a field is tracked
1) Added some fixes and additional tests for #tracked_changes and #tracked_edits, as there's a pre-existing hack described in Issue #69 which requires us to flip-flop the :from and :to values for the specifically for :destroy action

2) Refactor and test #trackable_parent_class method, which returns the parent class of the trackable regardless of whether the trackable itself has been destroyed
Merge pull request #70 from johnnyshields/master

Trackable#tracked_fields + fixes for Tracker#tracked_changes + Tracker#trackable_parent_class