Added the possibility to choose the serialization technology between ROOT and PB, and a new convention for FilterUnit.
Added methods in DQMFileSaver for saving ROOT and PB files in FilterUnit convention, and PB files in Online convention.
Remove emacs local variable definition in DQMStore.
Support all cases for conventions and file formats, and use the corresponding functions in DQMFileSaver.
Added JSON file creation.
Changed enum data member name from serialization to fileFormat: files are saved in different formats, but objects are always serialized via ROOT.
Improved comments in the code.
Fix indentation.
FilterUnit convention can save files only at lumi boundary.
Make Convention and FileFormat enums public (in order to be used by static functions in the source file).
Remove code duplication for Online and Offline conventions: added static function for generating file names for ROOT and PB format, modified doSaveForOnline for saving the contents of DQMStore for ROOT and PB format.
Remove code duplication for FilterUnit convention: added static function for generating file names for ROOT and PB format, modified saveForFilterUnit and saveForFilterUnitPB for saving the contents of DQMStore for ROOT and PB format.
Added the DQMFileSaver configuration parameter for setting the file format.
Merge pull request #3786 from diguida/rebase_fastMergerPB

DQM -- DQMFileSaver capabilities for FU