add authenticated User LangPreference tracking

+ Use User.LangPreference when there is no set AURSID
  if request.user.is_authenticated is true.
+ Updated post /language to update LangPreference when
  request.user.is_authenticated.
+ Restore language during test where we change it.
+ Added the user attribute to aurweb.testing.requests.Request.

Signed-off-by: Kevin Morris <kevr@0cost.org>

test/test_accounts_routes.py

@@ -54,7 +54,7 @@ def test_get_passreset():
 
 
 def test_get_passreset_translation():
-    # Test that translation works.
+    # Test that translation works; set it to de.
     with client as request:
         response = request.get("/passreset", cookies={"AURLANG": "de"})
 
@@ -68,6 +68,10 @@ def test_get_passreset_translation():
     # And the button.
     assert "Weiter".encode("utf-8") in response.content
 
+    # Restore english.
+    with client as request:
+        response = request.get("/passreset", cookies={"AURLANG": "en"})
+
 
 def test_get_passreset_with_resetkey():
     with client as request: