Bug 578486: Resolve metamodel proxies during back conversion after the migration

* Extend BackwardConverter to resolve proxy URLs that point to the
migration metamodel because it will no longer exist once the migration
is finished.
* Load Resources with UUIDs in MetamodelUtils to allow referencing
elements in a stable way: UUIDs don't change when an element is renamed.
* Add DynamicEcoreFactory but don't register it automatically. This
allows clients to register it if needed but does not change existing

Change-Id: I40a5da6b1905c8505ab85e13ec6e204d7e713153
Signed-off-by: Lucas Koehler <lkoehler@eclipsesource.com>
3 files changed