Fix generation of MvdDigi in event based mode

Flush the internal buffer after each event when running in event based mode.
This creates digis for all channels even if the dead time of the channel is
not yet reached. All digis are written into the current timeslice.
Flushing the internal buffer after the last event when running in time based
mode to avoid losing data.
Create and send digi matches only if required. Should fix a memory leak.
Add LOG information in the init about run mode.
Remove obsolete code.