H5 writer for jets

I'd like to have a jet / IParticle writer in common for a few applications:

• Easyjet H5 outputs. This was taken from easyjet as part of easyjet/easyjet#121.
• The flavor tagging training pipeline
• The prompt lepton id training pipeline (which was based on the flavor tagging one)
• Unit tests for some flavor tagging tools within Athena

The first three could technically be accomplished with a submodule shared between all the packages, the last not so much.