Remove blur/focus feature

Recent changes to event editing removed the ability to change
"blurEnabled" for events, which bit us hard in a large-scale event.
Additionally, the $(window).blur strategy for detecting blur didn't
properly handle interactions with the youtube video, leading it to have
less utility.

We may consider re-adding it in the future but for now have decided to
remove it, and the concommitant feature for flashing the window title on
new chat messages.
Remove video group scrub control, fix perms

Remove the logic that would attempt to infer when an admin had
intentionally scrubbed a video in time, due to its fickleness.  Instead,
admins must manually "Pause for all", then scrub the time slider, then
"Play for all" if they wish to scrub time.

Fix handling of permissions for sending group control. Event page video
embed was allowing unprivileged users to send control messages (which
were being dropped by the server; but are nevertheless unnecessary
traffic).
Don't toggle intend-to-sync if the video is ending

If we get a 'pause' signal early because the video is ending and we're
playing a couple seconds ahead of the sync signal, don't toggle
intend-to-sync.