[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.
it can be - then it needs to be returned by the formatter.

is it important?