Selectize fields in agg builder

Make fields "searchable" via Selectize.

- Replace `angular-ui-select` with `angular-selectize.js`
  - `angular-ui-select` refused to work on fields, and the API was a huge pain
  - `angular-selectize.js` has a much better API, worked brilliantly and doesn't lock up FF
- Use selectize for include/exclude filter flags
- Use selectize for field selection
- Tweak styles so `selectize` inputs match vanilla inputs

Chrome:
![2014-12-18 16_12_47](https://cloud.githubusercontent.com/assets/404731/5497622/bdc8be28-86d0-11e4-81c2-e9b9d18325ca.gif)

Firefox:
![2014-12-18 16_20_15](https://cloud.githubusercontent.com/assets/404731/5497722/c8697aec-86d1-11e4-84cb-198b60b01151.gif)