PowhegControl (and EvgenJobTransforms): changes for lhe only prod (21.6)

Hello,

As discussed in today's GIT meeting, I making this MR to remove the automatic 1.1 factor wrt. maxEvents for the number of events generated by Powheg, for the case of lhe-only production (i.e. when no EVNT is requested). So in official production, we would get as many events in the lhe file as requested in nEventsPerJob. The behaviour in the "standard" production where an EVNT is requested will be unchanged: Powheg will generate 1.1 times the numbers of events requested in maxEvents, as standard safety factor. As mentioned in the meeting users can always bypass this by setting nEvents explicitely (with whatever safety factor is needed) before generate().

As a bonus: I modified EvgenJobTransforms to print the number of events in the lhe files in the log.generate (a MetaData line which can be picked by AMI) also in the case of EVNT production when the TXT is also saved. At the moment this print was only done in TXT-only mode.

Tagging @strichte @dhayden for PowhegControl, plus @mcfayden and @zmarshal for MadGraphControl (since we discussed consistency between the two during the meeting)