CR1: Improve RViz API and package structure

Customers

• Plugin developers
• Rviz developers

Current state

Plugins directly communicate with the RViz API and Ogre. They have access to all headers in RViz.

Problem Description

The process of how to create such a plugin is not well documented, as is the RViz API. There is no clear notion of what part of the RViz API should be accessible to Plugins. Changes to internal rviz source code can easily break plugins.

Proposed Solution

• Document how to make an RViz plugin
• Review RViz API and separate stable part that the plugins are supposed to use
• Break up RViz into separate libraries