Fix for centerPanel animation

Added `UIViewAnimationOptionBeginFromCurrentState` when animating
the centerPanel. This fixes glitchy behavior when there is a
`UIToolbar` in the centerPanel with a overridden
`layoutSubviews`. Without this option the buttons in the
`UIToolbar` would be jumping around before animating into place. It could
probably fix animation problems in other subviews with overridden `layoutSubviews` as
well.