Added: ability to specify transition easing (for ViewStacks etc)

**Linear.easeNone** looked a bit harsh for ViewStack transitions, especially for mobile apps. You can now specify.

Nice and smooth (higher stage.frameRate recommended):

    <ViewStack
        trans:Slide-direction="'left'"
        trans:Slide-duration="0.4"
        trans:Slide-easing="'Expo.easeOut'"
    >