FIX: Make autotag watched words case insensitive (PR #13043)

The ‘autotag’ words were shown even if tagging was disabled.

This commit also fixes the bug when no tag was applied if no other tag was already present.


How about we only filter the actions when tagging is disabled?

   SiteSetting.tagging_enabled ? WatchedWord.actions.keys : WatchedWord.actions.keys.filter { |k| k != :tag }