Add special case handling for draft messages so that if a Draft is
updated via an event it is correctly updated on the IMAP client via a
the new `imap.MessageUpdated event`.
This patch also updates Gluon to the latest version.
We were closing the event QueuedChannel objects in the wrong place;
they should have been closed on test teardown, not on stopBridge
(which was just a test action and wasn't always called).
In order to make the events more scalable, i replace all the
QueuedChannel objects with a single event collector, which would
create QueuedChannels on demand when it receives an event of a new type.
