Two much needed bug fixes for Cointhief

I fixed the annoying behaviour of launchpads being innefective while falling, as your velocity was only being added to, rather than being set to a fixes force upwards. This made it so if you were falling, and had a big velocity pointed downwards, the launchpads would barely launch you up. I've now made sure the force you get is always at least be a full launch. You can still stack launchpads, but you will never lose out on velocity.

I also did a fix for level 5 where you could get out of bounds and not be able to complete the level. I just added a big collision box (see image) that stops you traveling past the finish line. Cool beans!