base: default module in PACKAGES

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

* NOTE If you have modified PACKAGES in your overlay configuration you
  will need to append 'invenio.base'.

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>
babel: translation loading from PACKAGES

* Adds lookup for '/translations' directory inside defined `PACKAGES` in
  order to support custom translation strings.  (addresses #828)

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