Added support for /checkout/ flow.
This commit adds a few features:
- The ability to retrieve SSL certificates for the pages in the webview
- Allows the delegate to dictate whether the height of the content div
  should get fixed
- Nicer handling of javascript alerts
Fixed build for new code that assumed the modern runtime and Security
Framework was available.
Fixed build for new code that assumed the modern runtime and Security Framework was available.
Merge pull request #5 from blackpixel/master

* Added support for /checkout/
* The ability to retrieve SSL certificates for the pages in the webview
* Allows the delegate to dictate whether the height of the content div should get fixed
* Nicer handling of javascript alerts