First cut at a GUI framework for SANS applications. 

Modules should be put in the "perspectives" directory
of their main application when using this framework.

Documentation to come...

Dependencies:
	- Needs sans.guitools version 0.1.1
	- Needs sans.guicomm
	
To-do list:
	- Clean up about box
	- Clean up the _find_plugins() function to allow user-defined directory
	- Modify the get_context_menu() function to allow a plug-in to recognize
		its own plots.
	- Provide a hook for a general file loader for the various data formats
	- Add group flag to allow groups of plots (and exclude other plots with
		same units to be plotted in the same Graph. [DONE]
	- If there is only one perspective, drop the perspective menu.
	- If there is only one panel in the Panel menu, drop the menu.
	- Make legend transparent
	- Make sure that when a plottable is sent a second time for update, that we replace the lables too!
	- Add help menu entry for each module