Bitmap modes can corrupt allocators

[corwinkuiper]

Bitmap modes give access to vram, where allocators store state. This is bad.

Also, I don't think objects can be used in bitmap modes, and besides they share vram so allocation gets clobbered.

The fix:

• Initialise allocators on acquiring the resource.
• Objects and backgrounds come together, I think.

The current difficulty:

• I've used sprite allocation without resource acquisition a lot. Can be fixed but will make things more awkward.