Fix FT mat element and a few methods
Fixes the elementID in Detector (for DD4HEP)
Methods in FT will be changed from 'module()' or 'uniqueModule' to methods like:
- globalXID: unique (in global) identifier of X
- localXID: unique (within the parent) identifier of X.
IDs and Idx are made formally different. An idx is contiguous, and starts at 0.
Must be merged with Rec!3018 (merged), Allen!931 (merged), Boole!402 (merged), LHCb!3679 (merged)
Edited by Louis Henry