Shibboleth: make user properties mapping generically configurable

Today, the shibboleth user mapping can be configured, however only for a limited, hardcoded set of user properties. This should be refactored to a generic user property mapping similar to the configuration in the LDAP module. 

• Generic list of shib-attributes to oo-properties mapping
• Refactor code in ShibbolethDispatcher and ShibbolethRegistrationController and move user-sync code to a new manager
• Update all user properties on login (except username and language)

Special thinking must go into how to generically sync the following kind of user attributes: 

• multi-value shib attributes (save as comma separate oo-properties?)
• user language (code already there)
• gender (in UHH example an integer value)