Fix CGB-ACID2 test

Closes #30

See merge request !27

This allows background to take precedence over objects.
This completes the CGB ACID 2 test compliance.

There may be a performance impact involved.

Previously only new ROM loading operations would take into consideration the auto-mode.
This fix affects the SDL frontend only.

Fixes issue with node 20.

Performance optimisations

See merge request !24