SMP HLT DQM, basic config and single photon paths

Resubmission of #6144 with cherry-picked commits.

First commit of basic SMP HLT DQM. Configuration is based on same C++ code as Higgs DQM and contains only python configuration.

Also modifies Higgs DQM code slightly to allow DQM directory name to be configurable. Change was discussed with Higgs DQM developers, Hugues Brun and Sami Lehti.

Currently contains only single photon paths (proposed by SMP at Oct14 Strasbourg TSG workshop).

An example output file is here, including the new paths:
/afs/cern.ch/user/o/olivito/public/dqm/CMSSW_7_3_0_pre1/src/HLTriggerOffline/SMP/test/DQM_SMP_singlephoton_Hggrelval.root