[WIP] FlipView v2

Lots of changes to the FlipView.

- [x] Make FlipView MVVM friendly and fix #998
- [x] Fix focus issues
- [x] Fixes #1053 ([this](https://github.com/MahApps/MahApps.Metro/commit/04be29f9b6eee9ca05661874add7c6113f2f88f5) is already in our master branch). 
- [x] Selectable FlipView Transitions - fixes #1144
- [x] Add ```Orientation``` which would allow us to do something like this. (See the picture below depicting a vertical flipview. Its from the Windows 8 Store. **I accidentally resized the picture, which distorted it.**)
![flipview_vertical](https://f.cloud.github.com/assets/251501/2388050/d7c68fce-a93d-11e3-83b5-51cc7e1349b3.png)
- [x] Add simple W8-like glow.