Separate client code into separate repo

After long discussion on the netstack list, we've decided to split the quantum client code into a separate repo to be more inline with other openstack projects.

Note: there are obvious infrastructure, build, and documentation implications to this change. It will likely take a while to sort out, but we want to do this as quickly as possible so that distributions that package Quantum have time to react prior to the main essex release.

In doing so, we will likely need to duplicate some code currently in quantum.common. We should clearly mark any code we duplicate, with the goal of eventually eliminating this duplicated code by relying on a shared library like openstack-common.