access: removal of external authentications
access: removal of external authentications

* INCOMPATIBILITY Removes proprietary authentication protocol for
  robotlogin.  (closes #2972)

* INCOMPATIBILITY Removes external authentication engines. Please use
  `invenio.modules.oauthclient` or Flask-SSO instead.  (closes #1083)

Signed-off-by: Jiri Kuncar <2bdffcb416fed3002465740d19a053a39918cbe5@cern.ch>

inveniosoftware/invenio-base,tiborsimko/invenio-base,tiborsimko/invenio-base,inveniosoftware/invenio-base