Adds support for the Security Group extension to neutron

[minor] After calling `super(rule)`, would it instead be possible to carry out the checks on `this.direction` rather than `rule.getDirection()` etc.? After all, it's **this** object that we're really trying to validate, not the input rule.

Regarding the naming: see the similar comment for FloatingIP. `CreateOptions` sounds to me like an "options" object which is used elsewhere in jclouds pretty much only to _modify_ a request...not as a domain object.