Fix dissapearing surenames after updating personal data

Due to a security fix visitors are not allowed to change their surenames.
 However, this was only fixed by appending HTML-tag 'readonly':
 1) It's still really easy to this change your surename by just removing
    this HTML-tag in your browser.
 2) The surename data wasn't sent so the processing form (due to a not required
    field) return the surename as an empty string.

Eventually this views should entirely be processed by a modelform ONLY. So no more
 assigning cleaned data to specific fields of the request.user.contributor!