Provide setState and setNode notifications to the drivers

[davideaster]

Model drivers may need to know when setState occurs for the application--or setNode for certain nodes--if the driver has private state that it can't express in its properties.

When the state is refreshed in an existing client, the driver must flush this private state in order to be in sync with new clients that are joining.

• Declare the kernel and model and view driver API
• Call the drivers during kernel.setState and kernel.setNode.
• Send setState to all clients when new clients join.
• Look for bugs stemming from setState on existing clients (start with http://redmine.virtualworldframework.com/issues/2182).

[davideaster]

@rchadwic @eric79 FYI. This is still in progress.