Cleanup: Get rid of pootle_app/lib/view_handler.py

Fixes bug 3057
Cleanups
Tagging: Use AJAX for filtering TPs in project overview

Fixes bug 3070
Tagging: Fix table sorting when AJAX tag filtering is used

Fixes bug 3083.
Tagging: Add tagging support (list, add, remove) for stores

Fixes bug 3090