Allow for modifying geometry in geant4 overlap check

Motivation: some geant4 geometry overlaps are very very slow; mostly due to repeated small structures. We can disable (or simplify) these structures when running the geant4 overlap check, at least in regular CI runs. A nightly run can still test the full geometry.

Application: mrich fresnel lens, ecal fibers

Implementation:

• in athena.xml, add e.g. <constant name="ApplyOverlapCheckSimplification" value="0"/>
• in overlap_check_geant4, use sed 's/name="ApplyOverlapCheckSimplification" value="0"/name="ApplyOverlapCheckSimplification" value="1"/' athena.xml > athena_for_overlap_check.xml
• in e.g. compact/mrich.xml, use <detector overlap_check_simplification="ApplyOverlapCheckSimplification" ...
• in e.g. src/MRich_geo.cpp, use while ( groove_rmax <= full_ring_rmax && overlap_check_simplification == 0) { ...