Squashed commit of the following:

commit 6f135b3e9e4f843cf1c89ef8e4c95680e88b6807
Author: stephane brossier <stephane@ning.com>
Date:   Wed May 15 19:04:50 2013 -0700

    Rename module Gen -> Model

commit 5410560f9b23c58c9005a2b8c94a2db15fc32495
Author: stephane brossier <stephane@ning.com>
Date:   Wed May 15 12:23:34 2013 -0700

    Formatting

commit e58187dc2810cb3351f29301892ed3adffc4c319
Author: stephane brossier <stephane@ning.com>
Date:   Wed May 15 11:40:42 2013 -0700

    First gen for all killbill objects

commit 4c2207daaa021a8efa8fb88f9f38af56a9024598
Author: stephane brossier <stephane@ning.com>
Date:   Wed May 15 10:48:39 2013 -0700

    First gen for all killbill objects