Add resource locking requests

This enables the servers, images, load balancers, database servers and
database snapshots to be "locked" to prevent deletion.

When locked any API calls to destroy the resource are refused until an
unlock API call is made.
Add modular support for resource locking
Fix resource #locking? method

Also merges in data from response to ensure the data is no longer stale
so the `locked?` method responds correctly immediately after locking.
Fix 1.8.7 parsing and skip
Merge pull request #6 from brightbox/resource_locking

Add support for resource locking