Temporarily use ...client:dev-feature/list-second-factors.
Allow consumer to list identity's second factors.
Add SecondFactorService service definitions.
Correct second_factor_identifier key.
Allow consumer to list identity's unverified second factors.
Organise use statements.
Merge branch 'develop' into feature/list-second-factors

Conflicts:
	composer.lock
Return an UnverifiedSecondFactorCollection instead of an array.
Correct variable name.
Expose unverified and verified second factor collections.
CollectionDto#createElementFromData() returns mixed, itself.
Merge pull request #6 from SURFnet/feature/list-second-factors

Allow listing of second factors