[Design] - Prototype of ResourceModel

/cc @yishaigalatzer @harshgMSFT 

Not included here:
- Model Metadata integration
- Sample generation interface
- Filter interface for customizing formatters
- Xml Documentation access

Where possible I made decisions that are similar to webapi api explorer. See comments in the code for context on specific decision points and open questions.
If your actions aren't like ours, then you need to implement your own provider. 

If I add nancy or simple-web to MVC - then I don't want MVC treating those actions like the built-in ones.