Improve layout of POFile:+filter

Page like

  https://translations.launchpad.dev/evolution/trunk/+pots/evolution-2.2/es/+filter?person=carlos

should be improved in the following way:

 1. Translations should be grouped by date
 2. If there is more than one translation by that person on a single POTMsgSet, only show the latest one
 3. Colours should be fixed
 4. We should use bold text and check mark to indicate active translations, and cross mark to indicate rejected suggestions.

See https://devpad.canonical.com/~danilo/pages/pofile-filter.jpg as well (I need to move this to people.canonical.com/~danilo).