Added _getSurveyTakeForm to the Survey view. Subclasses can overwrite this method to create their own form. ProjectGradingSurvey will likely be an example for this.

Only initialize a SurveyTakeForm in take instead of in takeGet and takePost. This will allow for other subclassed views to easily replace the form the view is using. Also small style fix in Survey helper.

Split SurveyForm into SurveyTakeForm and SurveyEditForm. This allows for a more cleaner implementation of the Form code. And this will make it easier to break free from the getFields method in the future. Also the getRoleSpecifcFields method and the this_user and project variables have been removed. They are deemed obsolete. Reviewed by: Lennard de Rijk