Event builder new

Added new classes Cbm2021EventBuilderAlgo and Cbm2021EventBuilderTask in /reco/eventbuilder/digis. These classes are based on CbmMcbm2019TimeWinEventBuilder but used std::vector in the Algo class instead of accessing the digi manager. The vectors are filled in the Task class. CbmEventBuilderLinkDef.h and CMakeLists.txt are updated accordingly.

Comment: Currently the header file CbmMcbm2019TimeWinEventBuilderAlgo.h is included to access the utility classes EOverlapMode and EventBuilderDetector. Defining them directly in Cbm2021EventBuilderAlgo.h leads to a naming conflict with the 2019 version.