Improve on the event/trigger type flags

The flag e.isPhysics was initially implemented to mean both physics event type and/or physics trigger type depending on the data taking era. This migth be misleading. This MR restores the meaning of e.isPhysics to "physics event type" as before, and the "physics trigger type" is now the e.isTriggerPhysics flag. Also updated names of other flags to clearly indicate the relevance to trigger: e.isTriggerRandom and e.isTriggerBeam.

Added the e.isOnSpill flag to indicate the event during the burst interval, isefull for calibration (LED) events.