base: default module in PACKAGES

* Adds 'invenio.base' to PACKAGES in order to simplify application
  factory.

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
apikeys: fix for early import outside app context

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
assets: registry proxy usage fix

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>