Deeper HEK integration

[Malte Nuhn]

HEK provides rich interaction with eventdata - including user-feedback.

In order to make this functionality available in JHV, we should start with allowing to log into the HEK-API with his username and password.

If this is possible, the following things will be easy to implement, too:

- Rating Events
- Commenting on Events
- Adding a reference to an event
- Uploading an event to the registry
- Posting a revised event to the registry

And when it's ready inside the API - the most interesting thing:
- Reporting relations between events/features