Provides an option to bypass JS validation of user's postcode.

#### What's this PR do?
- Provides a theme setting to bypass JS validation of user's postcode

#### How should this be manually tested?
- Open [Paraneue Settings](http://dev.dosomething.org:8888/admin/appearance/settings/paraneue_dosomething)
- Turn off `Validate Post Code`
  ![image](https://cloud.githubusercontent.com/assets/672669/4941452/3ec48840-65e3-11e4-9899-1a07bec7ef48.png)
- Go to [Yeah, Science!](http://dev.dosomething.org:8888/campaigns/yeah-science)
- Click 'Get this banner, yo.'
- Fill in `M5H 3H1` to `Postal code` field. The field must not be highlighted in red after that
  ![image](https://cloud.githubusercontent.com/assets/672669/4941442/1fd8a9c0-65e3-11e4-96d6-4d142b255ec1.png)

#### What are the relevant tickets?
Closes #3329