Add translation, rotation and scaling control

[mfdorst]

glPushMatrix() and glPopMatrix() are deprecated, so I need some way of implementing local translation, rotation and scaling.
The proper way of doing this is to pass one or more matrices to the vertex shader, which will be applied locally to each primitive.
The easy way of doing this is probably to code for this stuff in the model. (The classes in model.shape would have members for translation, rotation and scale, and these would be applied in the getters for the shape's vertices.)
I should implement it the easy way now, and then later, when I start getting into more advanced shader technique I can refactor it to utilize the vertex shader instead.