Modified GUI to have auto filling

Gui checks including checking that bone density variable is a scalar and
located at the int pnts/centroid/elem nodes
Cleaned up GUI files
Clean up of pyvXRAY_plugin
Bug fixes in GUI
First start on updating virtualXrays to match GUI
Started major re-write to include assembly sets

Also added supported for different element types
Fix for element list from regions
Combined element maps from diff regions
Bug fixes for multiple element support
Bug fixes during testing
Remove use of dict.fromkeys

Uses same object when generating a dict of dicts
Bug fixes and cleaning up after testing
Bug fixes after testing
Merge pull request #8 from mhogg/Add_assembly_set_support

Add support for both part instance and assembly sets and more element types