Add a ``schema`` command to cmd ctrl to generate schema image. This changeset add the new commande and do some refactoring in cwconfig and schema.py to allow the use of CubicWebNoAppConfiguration with CubicWebSchemaLoader.

#!/bin/sh

rm -f web/test/tmpdb*
rm -f web/tali18n.py

rm -f applications/*/test/tmpdb*
rm -f applications/*/tali18n.py
rm -f applications/*/i18n/*_full.po
rm -f applications/*/data/Schema.dot