Tagging: Align the tags to progress bar column

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.
Tagging: Hide tags by default & save their visibility state
Tagging: Add a way for removing a tag from a TP

Fixes bug 3054
Tagging: Add a way for removing a tag from a TP in project overview

Fixes bug 3076