Merged requested to merge fix-detector-environment into master
The first attempt at fixing Moore#417 (closed) (Detector!171 (merged)) missed the target.
To be able to have ROOT dictionaries that include header files from Detector we must have the Detector include directory to
ROOT_INCLUDE_PATH. This MR makes LHCb take responsibility of it since Detector is not based on Gaudi.
Closes Moore#417 (closed)