UK SSO: Store Postal Code in local database.

#### What's this PR do?
- Saves Postal Code to the local database during automation creation of local users from remote SSO

#### How should this be manually tested?
- `drush en dosomething_uk`, setup 
- Set `dosomething_uk_oauth_url`, `dosomething_uk_oauth_key`, `dosomething_uk_oauth_secret` variables
- Register and check your profile
![screen shot 2014-10-06 at 11 18 35 pm](https://cloud.githubusercontent.com/assets/672669/4532807/8b1ccf82-4d96-11e4-8601-367c9985ec8c.png)

#### Any background context you want to provide?
- it still not possible to see or edit it on the profile edit form
- as a side effect it hides Country: US from UK users

#### What are the relevant tickets?
Part of refactoring [#DS-381](https://jira.dosomething.org/browse/DS-381).