Implemented optional modular build:
- triggered with FAIRROOT_MODULAR_BUILD option
- does not require the environment variables SIMPATH and FAIRROOTPATH

Implemented optional modular build:
- triggered with FAIRROOT_MODULAR_BUILD option
- does not require the environment variables SIMPATH and FAIRROOTPATH
Merge branch 'dev' of https://github.com/FairRootGroup/FairRoot
Migration of MC classes for multi-threading:
- RootManager and Logger not yet ported