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, as described in an issue (see below). The control now mimics the button of the ToggleSwitch found in the Windows Store apps, including the *drag over the entire button*-feature.
![toggleswitchbutton](https://cloud.githubusercontent.com/assets/6247359/5073684/082b3276-6e84-11e4-990b-f31127ac5220.gif)

Fixes #1595 and #1466.
Just noticed a bit too late, that this is hardcoded to black and won't play well with the dark theme