Tidied up the IDE section

Repaired broken links. Removed some projects that are so dead, you can't even find traces of them in the net anymore.
Xamarin Studio isn't a fork of MonoDevelop, it's vanilla MonoDevelop bundled with Xamarin's iOS/Android addins (see [here](http://mono.1490590.n4.nabble.com/Is-monodevelop-really-Xamarin-Studio-now-td4663295.html)). As this is a common source of confusion, I'd prefer we make this clear here.