Fix some filter bugs (#4501)

closes #4499 

This restores support for v1 filters. The problem was that the state was
uncoditionally set to error instead of checking the v1 response.
While checking the code I found some other problems:
- Two error messages that were shown to users were not translatable
- When filters were updated sometimes `PreferenceChangedEvent` was sent
instead of `FilterUpdatedEvent`
- The notifications fragment was not listening to the
`FilterUpdatedEvent`

app/src/main/res/values/strings.xml

@@ -48,6 +48,8 @@
     <string name="error_blocking_domain">Failed to mute %1$s: %2$s</string>
     <string name="error_unblocking_domain">Failed to unmute %1$s: %2$s</string>
     <string name="error_status_source_load">Failed to load the status source from the server.</string>
+    <string name="error_deleting_filter">Error deleting filter \'%1$s\'</string>
+    <string name="error_saving_filter">Error saving filter \'%1$s\'</string>
 
     <string name="title_login">Login</string>
     <string name="title_home">Home</string>