ARR: Submission previous_url validation

[melisabok]

The pre process validation that checks if the previous_url is valid doesn't fail when the user pass the forum id + plus comment id:

id=[forum_id]&noteId=[note_id]

To fix this we should check the note that we get has an invitation that correspond to a submission and it is forum note (id == forum).

I would also request the users to enter the full url, the UI knows how to render the link to the previous forum.