Prepare for next app evolution

Add options to use draft v4 and/or id.
Utils: remove now unused function
Minor code change
New class JsonSchemaFactories

This class initiates 4 factories, depending on the chosen draft version and
whether we trust "id".
Enable different checkings (draft v3/v4 and inline addressing)
Some code changes, some more testing

Unfortunately, mockito cannot test final classes. Argh.