[WIP] MetroDialogs v4

### Todo list
- [x] Remove SizeToContent stuff. I have no idea why that was there. See #881 because it was the temporary solution until I removed this.
- [x] Write a simple ```InputDialog```. **If you want more features, take the code and modify it to your needs.**
- [x] Fix accented dialog's transparency.
- [x] ```RequestClose``` works for internal dialogs too. It is now called ```RequestCloseAsync```.
- [x] Added ```UseAnimations``` property to disable the animations on dialogs. This does not affect the overlay animations.


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FIXES #906