Allow UUID definitions in the mappings JSON

Add support for reading the Widget invariant and version UUIDs from the
TOSCA mappings JSON. In this commit the artifact-generator.properties is
also read and used to provide default values. This step prevents any
existing deployments (e.g. automated test integration) from failing.
The redundant properties file will be deprecated in a future commit,
only when the JSON configuration has been updated.

Also remove two unused Java files to help with coverage stats.

Change-Id: Idc82e28092a2b028214225c7974db411c9f8a173
Issue-ID: AAI-2284
Signed-off-by: mark.j.leonard <mark.j.leonard@gmail.com>