Window Buttons overlap Flyouts

MetroWindow will show the Min/Max/Close buttons over Flyouts that are open and have Position=Right, like Github for Windows.

## Github for Windows
![f1](https://f.cloud.github.com/assets/251501/933752/54915efc-005c-11e3-81ce-7e26be3ee732.PNG)

## MahApps.Metro
### Before
![f3](https://f.cloud.github.com/assets/251501/933844/89c0118e-005e-11e3-9db7-a7fdff2e6a58.PNG)

### After
![f2](https://f.cloud.github.com/assets/251501/933753/548f6d4a-005c-11e3-8734-9d6710bd52a9.PNG)