CPAlgorithms: add ability to select events based on global trigger matching in the EventSelection block

As requested by @katharin, this MR adds a keyword "GLOBALTRIGMATCH" to the EventSelection block, to request trigger matching at event-level. One can also ask for any event-level selection flag with EVENTFLAG someSelection_%SYS%.

We also make the global-trigger-matching output branch systematics-dependent, which is formally more correct (even though it's a small effect). Since the trigger matching can now be fully integrated into an event selection, the user can rely on the event selection flag and filter out the global-trigger-matching branches.