[WIP] RFC: Universal Renderable Entities

[baiirun]

WIP on Types vs "Renderable" types

For example, the Entity with the name "San Francisco" can be defined as having a "Place" or "City" type. The Geo data service indexes a subset of types to expose a Universal Renderable Type. This enables us to use the Entity NVT to describe many different types of Values. An application might decide that an Entity NVT referencing an entity with the "Place" type should be rendered in a unique way. Universal Renderable Types provide this abstraction.