CbmAlgoBuildRawEvents: Use bool flag instead of negative TS time values to trigger reading of TS meta data from file.

Instead of implictly assuming the presence of TS meta data in input branch when SetTsParameters() is called with negative values, a boolean flag is now used to decide whether TS meta data should be expected. This is true by default, but set to false whenever SetTsParameters() is called with any value, so supplying any external parameters leads to ignoring of the TS meta data array.

This allows to choose negative starting times for timeslices, which is sometimes necessary for input data from event-based simulations.

To run in event-based mode (one timeslice per event), it is recommended to use a symmetric time interval, e.g. by calling SetTsParameters(-1.e7, 1.e7, 0.0).

Furthermore, the trigger window for the reference detector should cover strictly positive times in this case, to avoid missing events at the start of the timeslice, i.e. SetTriggerWindow(ECbmModuleId::kSts, 0, 100) (the seed window is shifted into the positive domain by default, to make use of time slice overlap in time-based mode, which can cause problems in event-based mode).

@p.-a.loizeau @f.uhlig @v.friese Fixes the issue of missed events in event-based mode.