[ticket/12393] Make sure user can't open more than edit window per post

The event that would be triggered is removed from the elements events.
It will be added again once the edit has been cancelled.

PHPBB3-12393
[ticket/12393] Only let the user open one quickedit box

Opening more than one quickedit box doesn't really serve the purpose of
quickediting a post. This will prevent the user from doing so for now.
In the future, one might actually want to remove the click event from all
edit buttons to prevent this though.

PHPBB3-12393