Centralize requires into main files

So far some requires, especially for common methods in DSL shoes, have been split across a multitude of files. I moved most of them to their respective "top" files e.g. `shoes`, `mock` and `swt`. There are exceptions for files that we don't need all the time (`cli` and `help`) as well as files with dependencies just for that file (sound.rb depends on some sound only JARs).

I also extracted a `RectPainter` class from `Rect` - it was used in 2 other classes (background and border) so it really deserved its own class :-)

Oh yeah and I try to keep the requires in alphabetical order to have a good overview.