L1: optimizations of the reconstruction time

Several improvements in the CA tracker to minimize the reconstruction time also in debug-with-mc mode:

• new subslice splitting algorithm that searches in partially disordered data
• move the split in sub-timeslices from the CbmL1 level to the tracker core
• in debug-with-Mc mode with event builder: read only those MC events that are related to the current reco event.

In addition, many cleanups. In particular, the "legacy event mode" is removed.