mGerrit: *Block Diff Viewer on AOSP & Gerrit-Review

Apply MonoSpacing to diff viewer
 (https://developer.android.com/reference/android/graphics/Typeface.html#MONOSPACE)

* For now. Seems the api has depreciated without notice
  or new DiffApi's are blocking /revisions/current/patch
  for AOSP & Gerrit-Review
* Api's are noted as changing so we may need to wait till
  they stablize before recoding call revision based api's
  (which return base64)

Change-Id: Icce094e4ed862f4c2c93573df99c151e3387d9ba