In STS unpacker, fix bug in handling of TS_MSB cycles happening at edge of MS + cleanup

• Replace all legacy hard-coded numerical values for the TS_MSB cycle size by a constant derived in StsXyterMessage from the data format
• Remove deprecated special cases in the handling of the TS_MSB messages which are not present anymore in the current CRI data format
• Do not update TS_MSB and TS_MSB cycle from the MS header when the cycle happened exactly at the end of last MS
• Recompute the TS+MSB in TS offset from the MS heder only when changing the Cycle or the TS_MSB from the same header
• Add static method to convert Message Type into human readable string
• Slight improve/cleanup of debug printouts and debug levels

Was leading to errors and a crash in mCBM 2021 run 1588 files node8_3_0123 and node8_5_0002

@v.friese this actually comes back to the parts where you had some questions a few days ago. I took the opportunity to make some of the cleanup we discussed then, hopefully it makes the code/comments a bit clearer.