list sharing implemented w. passing UTs & FTs; changes to apps.dashboard.urls, .models, .views & .tests.test_views to accomodate; functional_tests.test_sharing also ensures sharing visible in UX; templates/apps/dashboard/list.html & /my_lists.html updated with django templating & for loops

src/apps/dashboard/models.py

@@ -10,6 +10,12 @@ class List(models.Model):
         on_delete=models.CASCADE,
     )
 
+    shared_with = models.ManyToManyField(
+        "lyric.User",
+        related_name="shared_lists",
+        blank=True,
+    )
+
     @property
     def name(self):
         return self.item_set.first().text