[IGSTK-Developers] igstkView: new design

[Julien Jomier]

Hi all,

We've modified the class design for the Scene and the View so that now 
multiple views are supported. I've checked in a new example in the 
Sandbox called 'TwoViews' based on the HelloWorld application.

Basically, the scene now takes two arguments when adding an 
ObjectRepresentation: The first one is the viewer and the second one is 
the object representation. So we ensure that each viewer has its own 
ObjectRepresentation. I've also added a Copy() method in each 
ObjectRepresentation to help users.
Note also that the SetScene() has been removed from the View class so 
the View class is now "passive". That allowed us to remove some of the 
observers.

Luis has to clean some of the state machines with the new design but we 
are feeling better now ;).

I've also added some tests so the coverage is better.

BTW, the style guide looks perfect,

Julien