Too many functions, too different parameters, unnecessary DB queries.
All repositories developed for Moodle 2.3-2.5 will continue to work.
Also get rid of DB field files_reference.lifetime, it is not used by
anybody except repository itself.
Fields files.referencelastsync and files.referencelifetime just waste the space and actually duplicate the fields
files_reference.lifetime and files_reference.lastsync
Previously, even when a specific setting had to be returned, this method
would return an empty array. Now, the behaviour is the same whether
some options or none are set: if the requested setting is not found
null is returned.
