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

...tOutputModule and make the DQMRootSource a friend with DQMStore
hello chris,
the member is accessible only by the friend classes. it is not public
https://github.com/deguio/cmssw/blob/propagateEnableMT/DQMServices/Core/interface/DQMStore.h#L691

still not allowed? why?
thanks,
F.