[FEATURE] Allow authentication with partial OpenID identifier

Instead of forcing the user to enter her full OpenID identifier when authenticating,
a partial OpenID identifier, without the protocol, should be allowed.

Change-Id: Iae686d116b9c2ebae00d9818beeadf307b96f427
Resolves: #33518
Releases: 4.7, 4.6-backports, 4.5-backports
Reviewed-on: http://review.typo3.org/8764
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe
Reviewed-by: Xavier Perseguers
Tested-by: Xavier Perseguers
Reviewed-by: Stefan Neufeind
Reviewed-by: Steffen Ritter
Tested-by: Steffen Ritter