Add DetCommon project
To address the LCG layer issues observed in ATLINFR-3977, we decided to build a separate DetCommon project that can be used by CTP/L1Calo instead of the full athena release (unlike the DetCommon project of SVN days, this is a completely standalone project and Athena will not build against it). Its configuration is mostly a copy of AthDataQuality, i.e. the project does not build a separate externals project (it just does a checkout for the cmake code). The LCG dependency should be kept the same as the corresponding TDAQ release.
The MR also contains a few cmake fixes to packages that are included in its build. I.e. it removes the TrigConf standalone (SA) libraries as there is no need to have separate names now.
Edited by Frank Winklmeier