Updated ssl pinning mode to have default pinned certificates by default

Referencing #1385

Looks the there is method to load default pinned certificates, but its never actually called anywhere.

I've got a PR here to set the default pinned certificates when you use the `policyWithPinningMode:` method. It could also go in the `init` method if we wanted them automatically pinned for every method, but I'm not sure that is the best option.

I added two additional unit tests to verify the state of the pinned certificate array when creating a policy, and also updated the example project to use pinning.