Implement app group containers for Extensions

When setting an app_group_id in the cdq.yml file, the database url will now point to the shared app container. This allows for app extensions to access the same database as their parent app.

Additionally includes a workaround for use on iOS Simulator v6.1 which doesn't seem to behave correctly, as discussed here: https://groups.google.com/forum/#!topic/rubymotion/qDsNSf8NtXM Sorry that this part isn't the most elegant code in the world!