Added color-coding by status to MapReduce bar chart.

Summary:
Having to scroll through the long list of shards to see how many are still
running is really annoying. This change improves the bar chart to include
color-coding by status:

BLUE - In progress
GREEN - Success
YELLOW - Aborted
RED - Failed

Screen shot of an in-progress job (some shards have completed):
https://s3.amazonaws.com/uploads.hipchat.com/6574/48154/hU508blZbfrVtg8/upload.png

Screen shot of a failed job (one shard failed, other shards aborted):
https://s3.amazonaws.com/uploads.hipchat.com/6574/48154/87fvNmz26ywB3uB/upload.png

Test Plan:
- Start a MapReduce job
- Go to the MapReduce status page
- See pretty colors

Reviewers: mattfaus

Reviewed By: mattfaus

CC: tony, jace

Differential Revision: http://phabricator.khanacademy.org/D6343