Opening images and adding them to the scene

Signed-off-by: Rodrigo Goncalves de Oliveira <rodrigo@thecoreme.org>
Fix build using Qt 5.x

Just include widgets for qt5 and gui for qt4. In the future, we should
think about using the new elements instead of using the compatibility
ones.
Splitting scene related functions to its own class

Let the fun begin!

Signed-off-by: Rodrigo Goncalves de Oliveira <rodrigo@thecoreme.org>