Allow to define "tags" in RAML

[jarrodek]

OAS allows to define tags so the information rendered in the tooling (like API Console) can reorder the elements in a more meaningful was (from a designer point of view). There's no way to achieve the same goal with RAML.

It would be nice to have a feature that allows to define some kind of grouping. In case of a very complex APIs (which is quite romal for enterprises) such grouping would allow to alter the information architecture of automated API tools (API consoles of all sorts) that renders API in a GUI.

Related issue: mulesoft/api-console#507