The renderer should stop referencing bitmap resolution

[fsih]

A solution we considered: createBitmapSkin should take a width and height instead of bitmap resolution

Somewhat related: Right now the renderer is the only place where size and rotation center mean something different from in the other repos. We also retrieve the rotation center we use everywhere else from the renderer in loadCostume. This causes some complexity, so we might want to figure out how to make this simpler.