[Scenario] Address discrepancies in Activity's tag UI

nasa/MCT-Plugins#89 documents some aesthetic issues / visual discrepancies between the UI provided for adding/removing tags and the rest of the Info View. These issues are addressed here:

* Fix alignment, size, border, and focus background for the drop down menu used to add or create tags.
* Fix the width, vertical spacing, and title for the "create tag" dialog when adding a new tag.