Hundreds of tweaks

- SPB multiplier depending on 1st-2nd distance
- Removed the Battle-only k_poweritemtimer (hold over from when you could easily get invuln items all of the time), replaced it with a 2 invincibility item cap in ALL modes.
- Spinout is affected by boosters, *properly*
- Can no longer strafe while spinning out on speed bumps
- Messed with how other items interact with speed bumps, again.
- Old bounce code has been ported for non-players
- Fixed Karma players being able to do anything after the round has ended.
- Fixed sneaker and spinout timer weirdness
- Fixed Mines still being hold-use
- Fixed rubber-burn turn not working
- Removed redundant k_spinout and unused k_boosting variables
- Filled out the Color_Opposite table with Kart's new colors. Not really relevant right now (besides some extra Lua functionality) since nothing uses it, but will be nice for if we do the signpost from the sky idea.