Support for View Models

[vJoeyz]

Support for something like view models, perhaps in the same way statamic does it.

I've made a very very very rough poc here. I wasn't really sure where to put all that stuff. However, it does seem to work and hydrates the cascade given the view model defined in runway.php. I'm even less sure of how it can work with relations and caching.

[duncanmcclean]

If it works, feel free to submit a pull request and I can build on top of it when I get a chance.