Admin can enable filters on site level and change their settings.

For each context manager/teacher can overwrite filters settings from the parent context. In the most cases it is treated as "Disable this particular filter for this course" but it may have more comprehensive combinations such as "Disable filter generally for category but enable for the particular course".

filter_set_global_state() should trigger event (it is recorded in config_log atm)

filter_set_applies_to_strings() changes the configuration settings and will be covered in MDL-5160

filter_set_local_state() should trigger an event

filter_set_local_config() and filter_unset_local_config() also should trigger events. It will be more difficult to test because context-level configuration is not used in any of the standard filter plugins.

filter_delete_all_for_filter() and filter_delete_all_for_context() do not need events