Rewrite owf=auto code to be more general.

- Change the definition to be a bit more general. The mapping from resolution
  to owf frames stays mostly the same however, but should handle weird
  resolutions better.
- Move everything to config module.
- Fix handling of tiles. It had a bug where owf for tiles was always
  threads * 4/3 - 1. Works as intended now.
Set owf default to auto.