Flag changed diffs in rt-server results views

* This patch adds new views; previous result views are still available.

* The new commit link in the regressions/fixes view now takes you to
  a results view that flags skips/fails occuring in the new commit
  but not in the old commit. And the old commit link takes you to a
  results view that flags skips/fails no longer in the new commit.

* Overflagging (eg flagging too many diffs as new) is possible.
  Say a page edit changes lines in a way that we would think of the
  "same diff" occurring in "different lines." Then it's technically a
  new line-based diff, and will be flagged as such. This does not seem
  to occur too much in practice (and won't happen at all if, in the
  future, results are pinned to a specific page edit across test runs).

Change-Id: I95dafb77e83ad63b7f46de25d48f78ba19fd0704