Implemented optional modular build:
- triggered with ALICEO2_MODULAR_BUILD option
- does not require the environment variables SIMPATH and FAIRROOTPATH
Conflicts:
	devices/aliceHLTwrapper/CMakeLists.txt
Migration of MC related classes for multi-threading & code cleanup:
- Use of RootManager and Logger (not yet ported) inactivated on workers
- Removed unused AliceO2::Base::Module class