(Bug 45552) Add Unproofread filter for the Proofread view

* Add an 'Unproofread' filter in proofread mode alone.
* Hide this filter in translate mode.
* If there is no other filter 'Unproofread' is the filter for
  proofread
* Filter applied for this translate|!reviewer:#|!last-translator:#
  # is userId of current user.

Change-Id: Ida34f6f56f668fb1fe75146523e7a9c6f17d394c