Add context to dataset

[smarziano]

After the CUTGroup test, adding context about the dataset would be a very helpful enhancement. This relates to issue #213.

Instead of choosing just dataset name from a drop-down list when "Adding a dataset," adding context about what that dataset contains and what a user could learn from it (even an example search) could be extremely helpful to those people who are not familiar with using data.

This would be an opportunity to incorporate plain language (#192) and guide users without a huge lift to the data. Very rough example: "311 Service Requests - Pot Holes Reported Look at the number of potholes reported on your block, neighborhood, or zip code and see what has recently been done. You can see which potholes have been fixed "Pothole Patched."