Toggling pregrading and Identifying blank solutions

This merge request does two things:

• Automatically identify blank solutions (either multiple choice or not) and set a feedback option named 'blank' for each one.
• When creating an exam, there are three options to specify which questions should be graded automatically.
• Pre-grade a question again if a submission is reuploaded and is automatically graded (by 'Zesje')

The grading policy is specified in the following way:

• 0/set_nothing: Manually approve everything
• 1/set_blank: Automatically approve blank solutions
• 2/set_blank_single: Automatically approve blank solutions or solutions with one answer

Add a new field to a problem in the database with this number.

For a more detailed description, see #61.

Closes #33 and #61.

zesje/pregrader.py

@@ -7,18 +7,12 @@ from datetime import datetime
 from .blanks import set_blank
 from .database import db, Grader, FeedbackOption, GradingPolicy
 from .images import guess_dpi, get_box
+from .pdf_generation import CHECKBOX_FORMAT
 
 from PIL import Image
 from flask import current_app
 
 
-CHECKBOX_FORMAT = {
-    "margin": 5,
-    "font_size": 11,
-    "box_size": 9
-}
-
-
 def grade_mcq(sub, page, page_img):
     """
     Adds the multiple choice options that are identified as marked as a feedback option to a solution
@@ -80,8 +74,6 @@ def set_auto_grader(solution):
     """
     zesje_grader = Grader.query.filter(Grader.name == 'Zesje').one_or_none()
 
-    current_app.logger.info(str(zesje_grader))
-
     if zesje_grader is None:
         zesje_grader = Grader(name='Zesje')
         db.session.add(zesje_grader)