Use simplediff in web service and move diff functions into diff module

* For now the refineDiff function (which isn't being used, and
  contains references to jsdiff) is commented out and in the diff module.

* This patch is just for web service. Still to do: finish switching to
  simplediff in rt-test (html diffing), and use the diff module for rt-test.

Change-Id: I3f7ffefaf6d2f75847e667d850083f4ecf323f42
Merge "Use simplediff in web service and move diff functions into diff module"