fix(controller): disallow uppercase app URLs

Since Deis app names become URLs directly, they must match a regex like [-a-z0-9]+, as we test for at
https://github.com/deis/deis/blob/master/controller/api/tests/test_app.py#L100. But the regexes for apps in controller/api/urls.py use [-_\w], which does some nice locale adjustments but allows uppercase chars and underscores. This changes the regex to match the serializer's regex. We can incrementally add more locale characters as things require changing.

fixes #936