Migrate Tau HLT DQM to DQMGenericClient+DQMEDHarvester

Use DQMGenericClient to produce all but one of the efficiency TProfiles, and simplify HLTTauPostProcessor to produce only the remaining TProfile that can't be done with DQMGenericClient (i.e. "EfficiencyRefPrevious" plot, where eff(bin) = N(bin)/N(bin-1), inside the "HLT_*" folders).

Infer the location of first L3 tau filter in the paths by looking the filter inputs instead of the location of the L3 tau producer. This will be needed when HLT goes to unscheduled/multithreaded, when producers are no longer in paths (and it works with current menus).

In addition some cleanup and small fixes to axis labels of some plots.

The histogram contents should stay the same, as should the set of histograms except DQMGenericClient adds new "globalEfficiencies" histogram in each subfolder it produces efficiency plots to.

FYI: @mbluj