More levels

This pull request includes seven new levels, bringing the total up to 15 :)

All of the platforms in these levels are of the sizes listed in #29. Many of these levels encourage the usage of user-placed platforms, too, so have fun with that :) I also changed the order of the levels to hopefully provide a smoother difficulty curve.

Can someone add these levels to the installer filesystem as well? I'm using Visual C# Express, and I don't want to download a 2.1gb blob right now...

Also, have a screenshot :) This level does look familiar, but...

...oh it's Level 7 if you want to try it :p
![a familiar level](https://f.cloud.github.com/assets/1811645/433757/1bc0cb00-aeed-11e2-81a0-46ae6073726f.png)