MetroDemo overhaul [WIP]

I think that we all agree when I say that the current demo for Mahapps.Metro is crap.

Because of this, I'm currently working on a complete overhaul of the demo that is more usable.

This pullrequest is still a work in progress, I opened it for feedback :)

## Current status:

### Buttons

![buttons](https://f.cloud.github.com/assets/964691/548859/14730cbe-c2ed-11e2-8a46-961ff6e492a9.png)

### Text

![text](https://f.cloud.github.com/assets/964691/548860/1e7b85ba-c2ed-11e2-8f60-01a141a77515.png)

### Selections

![selection](https://f.cloud.github.com/assets/964691/548863/289ac5a6-c2ed-11e2-8a9a-5129231fdb0f.png)

## TODO:

**Remaining controls**
- [ ] Sliders
- [ ] Combobox
- [ ] Progressbar
- [ ] These other things that move

- [ ] Themes showcase
- [ ] Transitions
- [ ] Validations
- [ ] Link to the VS Demo