Dhalperi show datasets created

1. Editor page now shows you what datasets were created by a query and gives you links to download them. This fixes uwescience/myria#580.
2. On the Datasets page, we remove the download links for big datasets. At the moment, "big" is defined as 100M cells -- product of # rows and # columns > 100,000,000.

Requires uwescience/myria#582 on the backend.

Two screenshots:
For 1:
![screen shot 2014-07-22 at 5 31 22 pm](https://cloud.githubusercontent.com/assets/526415/3667289/bcf980f8-1200-11e4-969d-39369532e159.png)

For 2:
![screen shot 2014-07-22 at 5 30 25 pm](https://cloud.githubusercontent.com/assets/526415/3667285/9b7ed2b6-1200-11e4-9ff6-ade12f30291e.png)

FYI @billhowe @mbalazin this is already live on <https://demo.myria.cs.washington.edu>