Users cannot create an Ignore filter using Watch toggles when they are all OFF

Since XWiki 15.5 RC1 all Watch toggles are now OFF by default, users cannot create an Ignore filter anymore using the the toggles (unless at least one toggle is ON).

The Ignore filter needs to be created manually using the "Add filter" button from the Custom Filters section under the Notifications Preferences, but this may be advanced for most users.

An use case for this issue is that Mentions or other targetable events can only be stopped by explicitly ignoring a location.