everywhere: use different session cookie names

If the user is hosting the dashboard in the same domain as
their blog (with a nginx suburi, for example), the two session
cookies clash; logging into one service logs you out of the other.
With this patch, both have separate names.

Fixes https://gitlab.com/commento/commento-ce/issues/49

api/commenter_login_test.go

@@ -24,8 +24,8 @@ func TestCommenterLoginBasics(t *testing.T) {
 		return
 	}
 
-	if session, err := commenterLogin("test@example.com", "hunter2"); session == "" {
-		t.Errorf("empty session on successful login: %v", err)
+	if commenterToken, err := commenterLogin("test@example.com", "hunter2"); commenterToken == "" {
+		t.Errorf("empty comenterToken on successful login: %v", err)
 		return
 	}
 }