lovr.headset.setBackground;

[bjornbytes]

This refactors the new background layer types (cube/sphere) into a lovr.headset.setBackground function that can take an equirect or cubemap texture/images. Now there is just 1 layer type (quads) and LayerType is removed.

[bjornbytes]

• stereo backgrounds aren't supported yet, but could be.
• formats are annoying. you can't do lovr.headset.setBackground('sky.hdr') because that will load an rgba32f image, but right now layers must be rgba8. Runtimes do support other texture formats for layers, but rgba32f isn't supported everywhere. However, you CAN do lovr.headset.setBackground(lovr.graphics.newTexture('sky.hdr')) because this will do a texture blit, which supports format conversion. Hopefully we can smooth this out in the future.