propagate the enableMT flag from DQMStore to MEtoEDMConverter and DQMRoo...

...tOutputModule and make the DQMRootSource a friend with DQMStore
Ok, it makes sense and I agree. But basically all the classes which are friend with DQM store will have to stay so because they access methods which will be made private soon as soon as the transition to dqmedanalyzer finishes.