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

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

Fixes bug 3070
Cleanups
Goals: Add initial infrastructure

This adds a goal tab for TPs and allows creating and removing goals using
the same form and links that can be used for tags.

Fixes bug 3073
Tagging: Fix table sorting when AJAX tag filtering is used

Fixes bug 3083.