Add a way of showing the end of a moving platform

[CurryKitten]

Got a lot of feedback from Steam user h84ll1. Some of which is very useful - one of those is a comment he made about not being able to tell if his ball was about to cross where 2 moving platforms come together as there was nothing that signposted this. This seems like a very useful thing to do, so I'll change some of the art to show the edge of the platforms more obviously.

[CurryKitten]

Added a red border to the non-forcefield ends of the moving platforms to give people a much better idea of where the edges are.