TRT_GeoModel: code refactoring and cleanup
Affected classes: the Tool and both Factories.
The changes include: the removal of redundant functions and typedefs,
refactoring of the headers, switching to ATH_CHECK()
macros where possible,
switching to Gaudi::Property
in the Tool, formatting changes, etc.
No changes in the functionality are expected. This MR is an intermediate step in preparation for more substantial updates that will come in later MRs