Documentation based on RAML (design doc)

[jarrodek]

The app should provide a view for API documentation. When projects model will be replaced with RAML definition (#509) the app should:

• provide a way to create / edit a documentation separately for whole API, endpoints and parameters
• provide a way to view the documentation.
• provide auto-generated documentation based on endpoints and parameters definition (for example https://docs.travis-ci.com/api/?http#builds). In this case it can contextually display an example request. This example should be able to be presented in different formats (like HTTP, Node, C, Java, etc).

This is a sub-ticket for #756