Adds support for the Security Group extension to neutron

> It's a bit confusing. createOptions returns a builder that allows you to create a CreateOptions object.

Thanks for explaining - became clearer as I saw more of the code ;-) I'm still uneasy about the use of `*Options` as a name for a domain object class, even though with the intended usage pattern I guess it's meant to be hidden.

I just sent an email to the dev list - hopefully someone will have some bright suggestion...