Selection in tagging mode and actual filtering

Understood the confusion. Since @EmyrClement implemented the BLT selection filter as a [copy](https://github.com/BristolTopGroup/NTupleProduction/blob/master/test/makeBLT_cfg.py#L21) of process.topPairE(Mu)PlusJetsSelection instances with tagging mode switched off, trigger studies flags need to be applied to both tagging and filtering selections. This also affects switching b-tagging requirements to tagging mode, which works as expected now.

Also added an explicit requirement of existing isolated leptons in modified dilepton cut for Z selection, it only affects individual (not consecutive) cuts yet useful for monitoring/debugging.