JCLOUDS-138. Add CloudStackImageExtension support.
JCLOUDS-101 - Add SecurityGroupExtension for compute

- Adds the SecurityGroupExtension to compute, with tests and stub
support.
- Gets everything else to actually build against this.
- Unifies on compute's IpPermission/IpProtocol, eliminating EC2's.
- Converters from EC2/Nova/CloudStack SecurityGroup (and rules, for
the latter two) to the compute SecurityGroup (and rules, etc).
- EC2SecurityGroupExtension and tests.
- AWSEC2SecurityGroupExtension and tests - depends on JCLOUDS-99.