CameraManager

Used by the backend to store, using a QListResourcesManager,
backend camera entities create from frontend ones.

Change-Id: I974c3af5591d2750bd7de9f9ccc542bad95ce4f0
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>
Added CameraManager to Renderer and RenderSceneBuilder

Change-Id: Ie8609aab3b2163ed97da47bfc5949388f7ec49cf
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>
RenderSceneBuilder and Renderer using RenderNodesManager

Change-Id: Ie557547aacadcc5b01982761ca53995342d8b790
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>