Samples

Add samples to show how to use this library (as requested in issue #3):

- [ ] SimpleNavigation ([taken from Caliburn.Micro samples](http://caliburnmicro.codeplex.com/SourceControl/latest#samples/Caliburn.Micro.SimpleNavigation/))
- [ ] HelloScrens ([taken from Caliburn.Micro samples](http://caliburnmicro.codeplex.com/SourceControl/latest#samples/Caliburn.Micro.HelloScreens/))