Ckanext-privatedatasets

The main aim of this release is fix bugs:
- Fields `acquire_url`, `allowed_users` and `searchable` are only returned when the dataset is private.
- Fix license in JavaScript file.

- Add GNU Affero License

Typos fixed:
- `adquire` replaced by `acquire`
- `adquired` replaced by `acquired`

This is a bug fixing release. Bugs fixed:
- Database connection is initialized before deleting the list of users that have adquired a dataset when this dataset is removed.

This version includes:
- Use a table in the database to store the users that can access a specific dataset (users are deleted from the table when the dataset is deleted **even if it is not purged**).
- 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 including integration tests (Selenium).
- Organizations can also create private datasets that can be adquired by users
- Adquire URL and Allowed users are now checked when a dataset is created or updated.
- Label `PRIVATE` is only shown when a user cannot access a dataset.
- Label `OWNER` is always shown, not only when the dataset is private.
- Only active datasets are shown in the list of adquired datasets.
- A lot of bug fixes and efficiency improvements.

First demo version. This version includes:
- Users can create private datasets even if they are not included in an organization
- Private datasets can be marked as searchable or not
- Dataset admins can choose the users that can access their private datasets
- REST API to add users programmatically to the list of allowed users
- A label is shown indicating if the user has or not adquired the dataset in the list of datasets
- A new tab is included in the user dashboard containing the datasets adquired by the user