feat: use wuttaweb for get_liburl() logic

thankfully this is already handled and we can remove from tailbone.
although this adds some new cruft as well, to handle auto-migrating
any existing liburl config for apps.

eventually once all apps have migrated to new settings we can remove
the prefix from our calls here but also in wuttaweb signature

tests/views/test_settings.py

@@ -0,0 +1,10 @@
+# -*- coding: utf-8; -*-
+
+from tailbone.views import settings as mod
+from tests.util import WebTestCase
+
+
+class TestSettingView(WebTestCase):
+
+    def test_includeme(self):
+        self.pyramid_config.include('tailbone.views.settings')