Enable the ProjectSurvey and GradingProjectSurvey views in the core. Also add menu items to the program menu for easy access to these options. Reviewed by: Lennard de Rijk

Implemented taking ProjectSurveys. The user will first be served a list of all eligble StudentProjects for which the ProjectSurvey can be taken. After clicking on the list the key_name of the project is attached as a GET param and the code uses the normal take view with the hooks to let everything run smoothly. An extra access check method is required which checks if the Project mentioned in the GET param is a valid project for the current user. This check will run together with the isSurveyTakable checker.

Edit SurveyRecord model to not make use of different Survey property for each subclass. This does mean that a simple query needs to be constructed by hand whenever you want to query for every SurveyRecord for a specific Survey. However the naming is now the same over each SurveyRecord and it fits well into the rest of the design of Melange.

Made the CSV exporter for Survey not rely on the BackReferenceProperty in Survey.

Added getTakeProjectSurveyRedirect. This redirect is used when taking a ProjectSurvey.

Added the possibility to change the action of the form on the Survey take page.

Small style fix in Surveys helper.

Set required is True for StudentProject reference in ProjectSurveyRecord.

Removed obsolete if tag form take template.

Added hook methods to takeGet and takePost.