- using "athena"
 - this avoids any clashing with the reference detector libraries.

This allows for a frame to be defined as the subtraction of 2 trds.

	modified:   compact/vertex_tracker.xml

Fixed ce_GEM overlap

 - Added gem layer structure
 - Added support module and ability to change the module component TRD
 parameters from the default envelope values.

	modified:   compact/gem_tracker_endcap.xml
	modified:   src/TrapEndcapTracker_geo.cpp

 - CylinderTrackerBarrel_geo can be used to define detailed modules
 which are then placed in barrel array.
 - The modules are cylindrical segments of a tube.
	modified:   compact/definitions.xml
	modified:   compact/gem_tracker_endcap.xml
	new file:   compact/mm_tracker_barrel.xml
	modified:   reference_detector.xml
	new file:   src/CylinderTrackerBarrel_geo.cpp

 - Uses the TrapEndcapTracker geometry construction
 - Material thicknesses needs attention.