Allow auto creating new terms or selecting existing ones

* Fix taxonomy term integration
* Integrate with select2 on the Angular, so you can select existing terms and create new ones as-well
* Node and terms are created in a *single* request!

Needs some more cleanup, but already working!
![angularjs_form___site-install](https://cloud.githubusercontent.com/assets/125707/3669991/e55c19f6-123d-11e4-9a25-005dd0b5c8b0.jpg)

c&p error

```php
/**
 * Overrides \RestfulEntity…::checkPropertyAccess().
 */
```