sortable results table

@JackDougherty here's a first pass at the sortable results table

[![screen shot 2014-06-25 at 5 28 34 pm](https://cloud.githubusercontent.com/assets/919583/3392762/125e57b6-fcb8-11e3-8d2f-fe47d6bf53b2.png)](http://datamade.github.io/FusionTable-Map-2-layers/)

[Demo](http://datamade.github.io/FusionTable-Map-2-layers/)

### List columns
* School - `School` column with hyperlink to `Url`
* Grades - `GradeLevels` column
* Address - combination of `Address`, `City` and `State` columns
* Manager - `Manager` column
* Gain - image of `Gain_image` sortable by `Gain_numeric`

### Notes
* From a UI perspective, I found that using a button to toggle the map and list view to be better than showing both at once. I went ahead and implemented for this project.
* The code for customizing the list is a little complicated, so I [erred on being more verbose](https://github.com/datamade/FusionTable-Map-2-layers/blob/master/js/maps_lib.js#L326). Let me know if the code and comments make sense to you.
* Sorting on the image column is controlled by a `<span>` tag with an attribute of `data-value` for storing the data you want to sort on. In this case it is `Gain_numeric`, while an image `Gain_image` is displayed in the table. The code for this is in [jquery.dataTables.sorting.js](https://github.com/datamade/FusionTable-Map-2-layers/blob/master/js/jquery.dataTables.sorting.js)
* The `Gain_numeric` column in the [Fusion Table](https://www.google.com/fusiontables/DataSource?docid=1ga2XDlXm5uoH5Dx_jKWrMn-BgBGYsSnSRqDWBYou#rows:id=1) contains `NULL` values, which makes sorting on that value difficult. `NULL` values should be replaced with `0`

If you have any additional changes you'd like to make, keep this Pull Request open, add your feedback here and I'll add additional commits to this.