CI: Switch to LCG_96b
This MR switches from using individually compiled packages from the clicdp.cern.ch CVMFS repository to the SFT-provided LCG environment.
This entails:
- switch to docker base images provided by SFT group
- new compiler versions GCC8, Clang8
- removed support for Clang8 on SLC6, no LLVM SLC6 builds provided anymore, removed formatting checks on SLC6
- new ROOT6, Geant4 version (required updating unit tests)
- all modules now included, also LCIOWriter
- updated formatting using clang-format-8.0, updated git hooks searching for clang-format-8
Also:
- Docker deps image includes LCIO library now
- Docker image now features LCIOWriter
This fixes #127 (closed), #144 (closed) This closes !142 (closed)