Add migration for licence field.
implement Licence on event model, and in the output to json and admin
Merge branch 'develop'

* develop:
  implement Licence on event model, and in the output to json and admin
  Add migration for licence field.
Avoid nil-error on empty licence.
change link to point to edit instead of event.

And acutally allow to fire the link.
Merge branch 'develop'

* develop:
  change link to point to edit instead of event.
  Avoid nil-error on empty licence.