The data view no longer directly subscribes to IMAGE_CHANGED events.
Instead the controller tells it when to update (i.e. whenever the controller 
is told to display an image).  This simplifies the code and eliminates the 
problem of the first image not having its data displayed.
As a result of these changes, KeyValueListPanel no longer takes a callable 
to get its data.
Removed KeyValueListPanel class since it no longer provides additional
functionality over the ListCtrlPanel.
Merge pull request #103 from drusk/data_panel_startup

Closes #102.