- Now the scene is created empty, and the user has a button for adding new cubes.
- FIXME - Found error: sometimes, when transforming a cube, another one which is non selected, is also transformed.
	- Workaround: OpenGLCanvas class now keeps the last mouse position as a attribute, and it is updated when pressing or moving the mouse. This didn't solved the error.
- Fixed error.
	- Error: When transforming some cubes, another non selected was also transformed in the same way, but "virtually" (the second one draws itself next to the first one, but it really remains in its original pos).
	- Cause: I didn't understand the relation between VAO's and VBO's. I saw a VAO as a container for VBO's, but it's not. It keeps the format of the data, and works with the current VBO (they are not binded between them).
	- Solution: Binding the right VBO for each Drawable in its draw() method.