Review class Util.dart and Flame.dart

[erickzanardo]

Our Util.dart has a bunch of methods that could be moved, or some even removed, here I will list all the reviews that I think that we could do:

• fullScreen, setOrientation and all methods related to screen orientation could be elsewhere, like a device.dart or something like that.
• initialDimensions: I am almost sure that this method can be deleted, because of the GameWidget we have a better way to get the game size and this method can cause a lot of confusing
• removeGestureRecognizer can be removed as we have a better way of handling gesture now
• All the renders methods could be moved to the canvas extension.

About Flame.dart

• the init method could be on the same device.dart file mentioned above
• The initializeWidget method could be removed, since we have better ways to load things now (Game.onLoad, Component.onLoad), calling that method to enable loading things before the runApp will be less needed.

[erickzanardo]

Solved by #640