AKSubmission: Handle internal notes

When submitting an AK the owner can specify internal notes; these are not displayed in the detailed AK view. However, they can be seen in edit mode. As "internal"suggests a certain measure of privacy, this needs to be handled differently in the future. Possibilities:

• change the help text to make it clear that this is adressed to the organizer, but not private.
• don't allow editing, but rather treat as a series of "messages" to the organizer, that can not be edited, deleted or reviewed, but only added to.
• distribute a token to the person creating an AK that can be used to edit internal notes, everyone else cannot see, edit, or delete