Paying attention to following items:
* Overall parameterization -- will use for optimization
* Constant naming consistency
* Documentation via the comments
* Added new ci job which concatenates all the `<comment>` tags into `docs/detector.md`
* All comments should now be formatted to fit the appropriate section in the markdown file.

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

Squashed commit from Marshall

	new file:   ci_GEM.xml
	new file:   compact/ci_GEM.xml
	new file:   compact/ci_HCAL.xml
	modified:   compact/definitions.xml
	modified:   compact/display.xml
	modified:   compact/materials.xml
	modified:   reference_detector.xml
	modified:   src/cb_CTD_Si.cpp
	new file:   src/ci_GEM.cpp
	new file:   src/ci_HCAL.cpp

	renamed:    elements.xml -> compact/elements.xml
	renamed:    materials.xml -> compact/materials.xml
	modified:   reference_detector.xml