Cherrypicks "converts the slot machine over to TGUI" (MrMelbert#621)

This PR is the long-awaited de-soulification of the slot machine,
converting it over to TGUI. It also updates the jackpot, since it
appears to have been quite broken. It will now give all of the available
prize money plus 10000 credits. I'm fairly sure this is what was
supposed to happen, but I honestly could not tell, so if this ends up
being a balance change then so be it. Also adds a new funny kind of
jackpot when you get 5 bombs in the middle row. Other than that,
generally cleans up and updates some of the slot machine code.

The styling of the slot machine ui is nothing fancy right now, and I'm
open to suggestions about how the ui should look.