Add a manage multiquotes dialog

[Colonel_mortis]

A few members have requested that something is added to manage posts that are multiquoted, for example if they get to page 5 and find that something they quoted on page 2 has been addressed already, so they no longer need it quoted. Currently, the options are to go back through the topic to search for the post, which can waste a lot of time, and to remove it once they insert it into the editor, which doesn't work or is very buggy on mobile browsers (at least on Android), so adding a dialog linked from the multipost info float would save a reasonable amount of time.