Merge develop into master: New way to store the users that can access a certain dataset

From the orginal branch: 
* Now, a table is used to store the users that can access a specific dataset.
* Refactoring: new files has been created in order to create a more logic structure.
* Notification to add new users is now a CKAN action so the URL has changed from `/dataset_adquired` to `/api/action/dataset_adquired`.
* New tests
* Bug fixes

Additionally:
* Selenium tests
* More bugfixing
* Check URLs
* Check user names
* Private label is only shown when the user cannot access a dataset
* Only active packages are shown in the list of adquired datasets