Reclassified the examples in 3 categories:
- High level: demo using the scene node/facade object:
     examples prefix: osgartsimple
- Intermediate level: demo using access to the AR modules and manual setup of callback
    examples prefix: osgartinterm
- Low level: demo without using node callback or scene graph updated, old school/low level using standard procedural workflow or event-based
   examples prefix: osgartlow

- examples added:
Using a dummy video+ dummy tracker:
   osgartintermvideo
   osgartintermvideobackground
   osgartintermtracker
   osgartintermregistration
   osgartsimplescene
Using artoolkit:
  osgartintermregistrationartoolkit
  osgartsimplesceneartoolkit

- Renamed VideoConfig and TrackerConfig to VideoConfiguration and TrackerConfiguration
(following same syntax of File Name == Main Class Name )

- added a new dummyvideo directory in share (needed to run the examples).

- added a Dummy Video Plugin and a Dummy Tracker Plugin
(data are taken from SSTT and hardcoded: screenshot capture, projection matrix and transfo matrix)

- separated the udpate call to update and updateCB: this will allow to support low level programming (previous update using nodevisitor as argument).