MDL-33774 mod_label stores the content where it is supposed to

removed hardcoded checking for 'label' module type

changed label update script
MDL-33774 instead of checking that activity is label we check that it has view url
MDL-33774 filter_activitynames removed hardcoded label module type
MDL-33774 Reset filters caches between unit tests
MDL-31885 The activity name auto-linking filter should not create links to webpages it was created on
MDL-31885 Removed static caching from filter_activitynames

Caching does not save a lot, there are no DB requests in the filter anyway. But it prevents from applying different logic for different modules inside the course