LIL-223. Add related name for course & lesson fields of Course model

apps/content/models.py

@@ -9,12 +9,14 @@ class Content(PolymorphicModel):
     course = models.ForeignKey(
         Course, on_delete=models.CASCADE,
         null=True, blank=True,
-        verbose_name='Курс'
+        verbose_name='Курс',
+        related_name='content',
     )
     lesson = models.ForeignKey(
         Lesson, on_delete=models.CASCADE,
         null=True, blank=True,
-        verbose_name='Урок'
+        verbose_name='Урок',
+        related_name='content',
     )
     title = models.CharField('Заголовок', max_length=100, default='')
     position = models.PositiveSmallIntegerField(