functional auth backend; new get_user() method in authentication model & new accompanying test methods

src/apps/lyric/authentication.py

@@ -14,3 +14,10 @@ class PasswordlessAuthenticationBackend:
             return User.objects.get(email=token.email)
         except User.DoesNotExist:
             return User.objects.create(email=token.email)
+
+    def get_user(self, email):
+        try:
+            return User.objects.get(email=email)
+        except User.DoesNotExist:
+            return None # might also just pass (which = return None)
+