Create customer with plan. Closes #39

Squashed commit of the following:

commit 4baa10f5a9141f1e3e1b0c4b5e2bf030152b1b9b
Author: Gilbert <gilbertbgarza@gmail.com>
Date:   Thu Nov 7 09:51:46 2013 -0600

    More test coverage

commit 0051c35f05ca5dce7822e744c23a97b5932fba21
Author: Nerian <siotopo@gmail.com>
Date:   Tue Nov 5 16:46:40 2013 +0100

    Allows creating a customer with a plan