Adding GeneratorInfoSvc to hold global generator metadata and necessary changes in existing config fragments and jO examples

• A new GeneratorInfoSvc config is added that should hold metadata information
• Implementation of GeneratorInfoSvc in Pythia8Config and EvtGenConfig
• New configuration function for ParticleGunConfig with more inputs so that it's more easily accessible from jO. Implementation of GeneratorInfoSvc in the new config
• Update of test jO so that they conform to the new functionality
• sample.generators is removed since the jO should never set this (it will only be set by the config fragments)

Output:

13:24:46 Py:Gen_tf            INFO MetaData: generatorTune = A2 MSTW2008LO
13:24:46 Py:Gen_tf            INFO MetaData: generatorName = ['Pythia8(v.316)', 'EvtGen(v.2.2.1)']

cc @tadej @ewelina