Changes to the SquareProgressBar

Hey, we talked some time ago about a bug in your library. Since then I've made some commits to my for and basically changed  lot the underlying code quite a bit(+ also the sample). I've tested the new code and it should work.

The change is big(I've also removed some of the API) so I'm not expecting you to accept it in the repository, if you don't, I'll handle it on my own, just thought to let you know.

Lucian