Making Quark-Gluon likelihood conditions DB object

This is the first attempt at translating static ROOT files (which the authors wanted to ship with CMSSW) into CondDB objects. They will be stored in QGLikelihoodObject objects. There will be further test configurations once the objects are actually in the database, but for now the only test is writing to local sqlite files and reading again. This replaces ad-hoc functionality from #2820 with a more robust strategy.