Match Flyout animation with Windows 8

I noticed when I started using Flyouts that the easing function did not match the Windows 8 animation. I tried to change it using KeySpline, but I couldn't find the correct control points. Then I realized I also had Blend installed with VS, and I was pretty sure it had a GUI function to create a keyspline.

I experimented in Blend with key splines and found that a KeySpline with the points (0.25, 1) and (0.05, 1) matches the Windows 8 Flyout animation the most. So I changed the Easing functions in the Flyout theme XAML to those KeySplines.

I also removed the opacity change in the Flyouts, since I never saw an opacity change occur in the Windows 8 Flyouts.
Please don't change any code stylings in this PR