Add dimuon invariant mass chain to LS2 menu

Some modifcations to get a dimuon chain with invariant mass cuts running:

- Setup the sequence for the invariant mass so that it is independent of the muon reco sequences
- Set the chains step with the invariant mass cut to have multiplicity of one to avoid it being treated as a combined hypo
- Some minor fixes for the hypo alg to allow for one-muon-per-RoI, and to not overwrite the feature link
- Added a test chain to the menu and updated the references.