First try at B2G HLT DQM

Here is a first try at a B2G HLT DQM module. This is, for now, almost exactly the same as that of the TOP PAG (thanks to Elvire for the help!). As such, it already merges #4594. 

The paths currently monitored are: 

- HLT_Mu40_eta2p1 : B2G is a stakeholder
- HLT_Ele30_CaloIdVT_TrkIdT_PFNoPUJet150_PFNoPUJet25 : B2G is the primary developer


We will also have all-hadronic triggers delivered at some point, as well as monitors of the jet mass + X triggers.