[[DO NOT MERGE]] Enable performance endpoint sorted by runtime.

Creates an endpoint to visualize the slowest chronos jobs.

Allows users to see the (sorted) list of slowest chronos jobs by various distribution parameters:

You can sort by mean, median, 75thPercentile, 95thPercentile, 98thPercentile, and 99thPercentile by hitting the endpoint at /scheduler/perf/{whatever}

Returns a JSON of the form [ [jobname, t_millis], [jobname, t_millis], ...]

I'd just like some commentary before I make more progress - is this what the users wanted? I know we talked about some rudimentary tools.
![screen shot 2013-08-29 at 12 07 54 pm](https://f.cloud.github.com/assets/525770/1052517/6360cd68-10de-11e3-8632-2d923564d13d.png)

@brndnmtthws @hcai @andykram @krisr