[WIP] [RFC] MetroNavigationWindow

Created a MetroNavigationWindow and created an IMetroWindow interface to bridge the gap between MetroWindow and MetroNavigationWindow. Hoping to fix #692

It's not finished but yeah, it looks terrible:
![mn1](https://f.cloud.github.com/assets/251501/1321061/a54feb56-3392-11e3-8299-751cdb4f8185.PNG)