change the naming convention of CaloMETs

Continuing from https://github.com/cms-sw/cmssw/pull/3942, this PR still changes the naming convention of CaloMETs. 

In particular, this PR adds the definition of *caloMetM*, which is to replace *corMetGlobalMuons*. 

This change was originally planned for CMSSW_7_1_0 but hasn't been implemented.

We announced this change at the JMAR meeting on 24-Apr-2014:
https://indico.cern.ch/event/304145/contribution/0

We discussed this change at the RECO meeting on 17-Apr-2014: https://indico.cern.ch/event/313948/contribution/18