Only use bunch pattern table when necessary

In most cases, the number of pulses does not change during a run, and it is not necessary to rely on the bunch pattern table to extract data like XGM, BAM, digitizer traces...

We introduce functions get_sase_pId() and npulses_has_changed() and perform a check in the load() function, to see if the number of pulses has changed. If it has, the bunch pattern table is loaded by default. If not, it is not loaded.