Tagging: Add a way for removing a tag from a TP

Fixes bug 3054
Attempt to fix column width change when tag are visible

Instead of letting the browser calculate the width of the tags cell, we
calculate it ourselves so that it does not change when whether tags are
visible or not.
Cleanups

The data to be shown on templates must be retrieved on views
Tagging: Add a way for removing a tag from a project overview

Fixes bug 3076
Tagging: Don't reload the whole page when adding a tag to a TP in Project overview

Fixes bug 3075