Summary:
basically did my darnedest to pull out a TwoUp rendering view. Made a base class for the rendering views with "old" and "new" terminology rather than "left" and "right.
Future revisions will finish cleaning up the terminology within the DifferentialChangesetParser itself and more of the ideas within T2009.
Test Plan: been playing with differential all day
Reviewers: epriestley
Reviewed By: epriestley
CC: vrana, chad, aran, Korvin
Maniphest Tasks: T2009
Differential Revision: https://secure.phabricator.com/D4117
