Factory pattern added for using page objects.

The idea here is to provide a mechanism that instantiates page objects by using a simple factory approach. The idea for this is to allow code to take on a very common structure, making it easy to review and easy to build automatic checkers for. This approach is also nice for indicating workflows in a browser application.

There are two factory methods: on_view() and on().

The on_view() factory simply creates the page instance and uses the load() method to bring that page up in the browser. The on() factory creates the page instance but does not need to bring up the page in the browser since it's assumed the relevant page is already in view.
You can be too slavish by worrying about patterns all the time. My first goal is working functionality, which this is, rather than "perfection" of design. I'm a get things done kind of guy first and foremost.

I would argue this kind of functionality has demonstrable value not just in this tool but in others. My goal here is really just to bring SitePrism in line with other tools that are doing similar things that testers in the industry actively use. I'm more than happy to see an alternative implementation, however, if it's agreed the functionality itself is worth exploring.