diffs: replace compare controller with new html based diffs:

* side/side + unified support
* redesign of diff changes/operations
* added button to see file before the change
* auto collapses large diffs

refs #4232

licenses/diff_match_patch_license.txt

@@ -0,0 +1,14 @@
+Copyright 2006 Google Inc.
+http://code.google.com/p/google-diff-match-patch/
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.