Support !=, null checking in CQL

This works with typeahead. I also changed the display of null values from "null" to "-". Let me know if you have other ideas.

Display of null values:
![screen shot 2014-12-05 at 6 25 50 pm](https://cloud.githubusercontent.com/assets/98301/5324723/51ccf5dc-7cac-11e4-8996-6d5fd4a7db52.png)

Checking against null:
![screen shot 2014-12-05 at 6 26 08 pm](https://cloud.githubusercontent.com/assets/98301/5324725/56108816-7cac-11e4-9418-3528d1212b51.png)

Checking for not null:
![screen shot 2014-12-05 at 6 26 18 pm](https://cloud.githubusercontent.com/assets/98301/5324728/5db90e1c-7cac-11e4-83b0-326d32406dd3.png)

Fixes #340 
This looks like (I realize it isn't) a typo--why not call it `'NOT NULL'`?