Make Graphic::draw(...) const

[qualiaa]

Allowing rendering to affect game logic can lead to unexpected side-effects when, for example, rendering the game while in a "paused" state.

To make this change, FrameList::draw() cannot change the frame of the animation, nor can it check for the elapsed timer's state, making this an awkward issue.

We should potentially allow Entity::draw() to be non-const, to allow users to do non-const things at their own discretion - thoughts?