Draft: helpers to compare geomodel subtrees, material validation
Tentative implementation of algorithm to compare subsets of a GeoModel tree, or separate GM trees. Importing generic code for mass evaluation and printout from MuonTrackingGeometry.
TODO : a) find out which part of the functionality is, or should be, handled by the GeoModel b) resolve crashes occuring in the readout of GeoFullPhysVol subtree from the database b) turn helpers into AlgTools for proper initialization ?