Fix compilation errors

No breaking changes.

* Updated dependency package names (e.g. `graphics` to `piston2d-graphics`)
* Fixed compilation errors, namely missing `#[deriving(Copy)]` directives now that `Copy` is explicitly opt-in.
    * The compiler warns about a few more structs that could be `Copy` but they don't need to be so I didn't change those.

I'll merge this myself in a few hours if the build passes and there's no objections.