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
refactor(controller): move app regex to settings
Merge pull request #1039 from deis/app-urls

fix(controller): disallow uppercase app URLs