improvement: make default url configurable at runtime (not just initialization time)

currently does not yet include methods to correctly trigger the new url, but its configuration and gets updated through scope.update_url

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
Merge pull request #4 from TelekomCloud/improvement/make-restangular-url-runtime-configurable

improvement: make default url configurable at runtime (not just initiali...