add create exam form to rapids

wally/models.py

@@ -5,15 +5,15 @@ def image_directory_path(instance, filename):
     return u"wally/picture/{0}".format(filename)
 
 class Specialty(models.Model):
-    specialty = models.CharField()
+    specialty = models.CharField(max_length=200)
 
 # Create your models here.
 class Candidate(models.Model):
     age = models.PositiveIntegerField()
-    specialty = models.ForeignKey(Specialty)
+    specialty = models.ForeignKey(Specialty, on_delete=models.SET_NULL, null=True, blank=True)
 
 class Response(models.Model):
-    question = models.ForeignKey("Question")
+    question = models.ForeignKey("Question", on_delete=models.SET_NULL, null=True, blank=True)
     time_to_find = models.FloatField()
     hit_point_x = models.FloatField()
     hit_point_y = models.FloatField()