First part of mCBM changes to data to monitors, tasks and unpackers

See commits messages for details

• Add gitignore rules for externals
• Support Legacy and Calib names for TOF in DigiManager
• Bring TimesliceMetaData to mCBM stand
• In raw StsXyter message class, adapt the error flags width and add enum class describing them
• Add PSD waveform fitting tools
• Bring monitor to mCBM stand
• Bring existing mCBM tasks to mCBM stand
• Bring TOF and MUCH unpackers to mCBM stand