Create witness model with associations to Incident model

Takes care of #4.

Has a really shitty privacy system at the moment

![screen shot 2013-08-13 at 4 56 07 pm](https://f.cloud.github.com/assets/740289/957925/dd7f0b4a-045a-11e3-8c04-84bccdc55daa.png) . ![screen shot 2013-08-13 at 4 56 29 pm](https://f.cloud.github.com/assets/740289/957931/e927cd1a-045a-11e3-922d-88e45f78e3ca.png)

When permissions are better implemented into the system, validations and privacy will be strongly cared for with respect to witnesses.

The idea is that witness names should be private only to administrators or moderators unless the witness gave an explicit *"okay"*.

![screen shot 2013-08-13 at 4 56 18 pm](https://f.cloud.github.com/assets/740289/957934/f1aca82a-045a-11e3-8845-fed683030733.png)