Rake task to dump TestResult data as CSV

To invoke, run the Rake task `rake test_result:dump`.

In theory, you should be able to run this off of Heroku: `heroku run rake test_result:dump`.

Example output:
```
"ID","Model","Test Type","Commit","Requested At","Started At","Real Time (s)","CPU Time (s)"
"3","knapsack_10_metrics_2.als","Performance","Unknown","2013-04-07 19:56:43 -0400","2013-04-07 19:56:43 -0400","25","10"
```

Reviewers: @cpkleynhans