Added mail template for when GradingRecords are proccessed.

Made the reminder templates extend the mail base instead of notification.

Added Task to process GradingRecords and update their StudentProjects. An index for this operation is required and has been added to the index.yaml file.

Added updateProjectsForGradingRecords to StudentProject Logic. This method takes a list of record_entities, processes them and batch puts the update StudentProjects.