Tagging: toggle filtering

Add an icon to toggle tag filtering widget.

Fixes bug 3077.
Tagging: reset the filter when hiding the widget

When hiding the filter widget the filtering is reset, and when
showing it again the filtering is restored back.
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
Goals: Add management command for adding project goals from a file

Fixes bug 3092