Impl of 'live' timers

Timers were added to the 'Live' and 'Replay' tabs of the control
panel.  These timers incorporated a change in display logic, and
the underlying implementation of simtime and polltime.

The 'Replay' control panel still needs alot of interface work.
Re-comment AJAX segment
Reformat retrieve_updates.php to return valid XML

retrieve_updates was previously returning a simple string whenever a new shot
was trilaterated.  This is insufficiently scalable.  Script output has been
reformatted to present XML formatted in the following manner:
<results>
	<shot id=# lat=# lon=# time=#>
		<sensor dev=# lat=# lon=#>
		</sensor>
		..(more sensors)
	</shot>
</results>