Add a new RDO persistent representation for sTGC

This update of the sTGC RDO format is required in order to use the calibration interface to retrieve parameters from the database and apply correction when needed. A new persistent representation _p2 is created for the sTGC, which has the unsigned integer variables time and charge. The STGC_RawData class is updated to include a second time variable to store unsigned integer value, since the old time variable of the type float is still needed for the near term.

The _p2 version replaces the previous _p1 as the default sTGC RDO persistent representation. Therefore, old samples might become incompatible.