DE-webapp Module refactor

This is a large refactor of the Discovery environment desktop code. 
A lot of unnecessary code, and resources were eliminated. 
The desktop code has an improved MVP implementation, with a clearer separation of concerns between view and presenter. 
The window management system has been simplified.
Many global events are no longer required due to the consolidation of functionality in the presenter.
The appearance pattern was implemented in many places, but more work in the regard is required.
A new theme module has been created, and most (if not all) of the appearance implementations have been moved there. Eventually, this theme module will be moved out of the de-webapp project.
At this time, there is a circular dependency between the de module and the theme module. While not critical at this time, this does need to be addressed if we want to upgrade to the next versions of GWT, which will have incremental compilation (potentially faster compiles in SDM).