Collapse set of messages to a thread.

Threads are a useful tool to encapsulate trains of thought  and allow members of the discussion to not ‘blow up’ a channel with a lot of messages.  Often, however, members don't realize a thread should be started and then by inertia the conversation ends up at the channel level.  Allowing users to retroactively create a thread would encourage better and more use of threads and save others that are not interested in the topic from spam.  Thus, I propose allowing the creation of threads from groups of messages that were recently created.  If messages are less than some time limit, i.e. 5 - 30min, then allow authorized server members to select a batch of messages to start a thread.