Add HotPlate and LiveUpdates stats

HotPlate card goes yellow when pending warmups exist. Otherwise it's green. 

LiveUpdates goes yellow if average time goes over 5s. 

We might have to tweak text size/layout to make the cards visible at a distance. 

commit bab205dff6d602014c6bc186fc76392b808dc604
Author: Chris Tweney <chris@media.berkeley.edu>
Date:   Mon Apr 7 10:52:17 2014 -0700

    Point at production Calcentral stats

commit c608f533bfddf20c3b606be4bf9e3103425e23d6
Author: Chris Tweney <chris@media.berkeley.edu>
Date:   Thu Mar 20 08:26:04 2014 -0700

    Add a warning state color, and make HotPlate stats and LiveUpdate stats use it

commit 441bf59c61ec504cd8c7be87158a4c93d694f2ac
Author: Chris Tweney <chris@media.berkeley.edu>
Date:   Fri Mar 14 15:49:30 2014 -0700

    Better way of defaulting STATS_URL

commit 522822314194c79a7b8ff3fdea8fe826539842a6
Author: Chris Tweney <chris@media.berkeley.edu>
Date:   Fri Mar 14 15:40:02 2014 -0700

    Parameterize STATS_URL and make display nicer for null data

commit 184b31717ad235db19825abffdbff0c33c121901
Author: Chris Tweney <chris@media.berkeley.edu>
Date:   Fri Mar 14 13:27:54 2014 -0700

    Add stats for HotPlate and LiveUpdates (currently pointed at localhost)