MDL-34290 update all references after the source is changed

MDL-34290 update all references after the source is changed

- When several records in {files} have the same record in {files_reference} and the synchronisation is performed, we need to update
all records in {files} so all files know if source is changed and that sync was performed;
- also when local moodle file content is changed we immediately update all files referencing to it (therefore sync of references
to the local files is unnecessary);