Rework "Plugins" dialog and some related code

This set of patches does several things:
* Merges the separate ITS and Segment plugin dialogs into a single dialog.
* Add additional information to the Plugins dialog for each plugin - version number and type ("ITS" or "Segment")
* Preserves the Export Data button from the ITS plugin dialog, but toggles its enable state depending on whether any ITS plugins exist and are enabled (in addition to a document being open)
* Changes the configuration XML to use the plugin classname rather than the display name.
* Minor text styling improvements to the Plugins dialog.