[Scenario] Add border to activity tag combo box

Begins to address UI inconsistencies documented
in nasa/MCT-Plugins#89
[Scenario] Pad activity tagging combo box

Add padding to give the tag selection combo box
a height similar to that of other combo boxes
in the Info View.
[Scenario] Hide empty tag area in Info View

If there are no tags to display, hide the tag panel
which would be used to display them in the activity's
Info View. Otherwise, this empty panel takes up a
few pixels of vertical space, causing alignment
issues for the label on the left.
[Scenario] Simplify activity tag combo box

Simplify activity tag combo box, creating the
always-there Add a Tag message using the
list cell renderer instead of "tricking" the
combo box with a custom editor. This has the
added benefit of restoring the default focus
color (previously missing)
[Scenario] Remove unused imports

Remove unused imports in ActivityVisualControl,
no longer needed after prior commits.
[Scenario] Widen text field in tag create dialog
[Scenario] Add space in tag create dialog

Add vertical space between the text field and
buttons in the tag creation dialog to match
UE design standards.
[Scenario] Add suffix to tag creation dialog
[Scenario] Move tag dialog strings to resource bundle
Merge pull request #90 from VWoeltjen/mctPlugins89

[Scenario] Address discrepancies in Activity's tag UI