ToggleSwitchButton rewrite

Well... most of the ```ToggleSwitchButton``` code has been rewritten. The animation of the thumb now resides in the code behind since the size of the button might change, according an issue (see below). The control now mimics the button of the ToggleSwitch found in the Windows Store apps, dragging over the entire button included.
![toggleswitchbutton](https://cloud.githubusercontent.com/assets/6247359/5073684/082b3276-6e84-11e4-990b-f31127ac5220.gif)

Fixes #1595 and #1466.