Update tooltips displayed on ComponentCell
Set up variable for storing model labels

It's a TreeMap, which maintains sort order. Neato!

I added some dummy values to work with, for now.
Add worker method to LabelsMenu to populate menu

It uses a nifty Map iterator.
Set up framework to add new labels to a model
Set up framework to delete labels from a model
Refactor handlers for adding/deleting model labels
Add "Manage labels" button to MoreActionsMenu