Improve tag selection pulldown

When adding a new tag in the tag column , the pulldown only populates with 5 tags, with no scrolling. The logic for which tags are in the pulldown seems murky. It is not the most recently used tags and it is not the 5 most used tags.

  1. Add scrolling.
  2. Provide some control over what is in the pulldown with properties. (Most used, last used, or manully entered.)