[WIP] [RFC] Introducing the 'TabBar'.

I have created a 'TabBar' which is a portmanteau for TabControl and SideBar. It's based on the control seen in the W8 Xbox Music app.

It's the menu on the left which has 'Collection', 'Radio' and 'Explore'.
![xbox_music_from_build-video](https://f.cloud.github.com/assets/251501/716171/e82c29b4-df30-11e2-9f1c-b2a0654d04cc.png)

I am writing a control that can acts and looks like that control:

![mam_tabbar_1](https://f.cloud.github.com/assets/251501/716199/536375d4-df31-11e2-87cd-ac78dddec876.png)


Of course, this is a WIP and I look forward to feedback in order to make this control the greatest 'visual' port as possible.