Add a metadata service and a test

[jmcarcell]

BEGINRELEASENOTES

• Add a metadata service that is automatically added when importing IOSvc from k4FWCore, if no metadata is added then the service won't do anything. If metadata is added, the metadata service will hold a podio::Frame with the metadata that the Writer will write. The metadata service only works when there is an output file.
• Add a test showing an example of its usage
• Make changes in the MetadaHandle to make it possible to save and read metadata from DataHandle-based algorithms, so that when switching to IOSvc metadata for existing DataHandle algorithms will keep working. Add a test using IOSvc with DataHandle algorithms that write and read metadata.

ENDRELEASENOTES

[jmcarcell]

This should now be ready and when using IOSvc it also works fine with DataHandle algorithms. I didn't bother with making it work when using PodioInput or PodioOutput and functional algorithms since that shouldn't be the case anyway.