Make EventAuxInfo_v1 members public

Hi guys,

I had an e-mail exchange w/ @ssnyder on this. Therefore, let me tag him as well. In this MR I basically make the members of the EventAuxInfo_v1 public, so that we can read some basic event information, such as the run/event number in plain (py)ROOT w/o the need of xAOD reading machinery.

Eventually, I'm planning to use this feature in a simple pyROOT script, where I'll be re-ordering CollectionTree content based on the event number. This'll allow us to easily compare two files written in MP/MT using the existing machinery.

I'll remove the WIP if I don't hear any objections on this.

Best, Serhan

Let me tag @emoyse @wlampl @jchapman @tadej whom I know are interested in this.