Add convenient method to create keyframe animations

[thecodewarrior]

Currently, keyframe animations are implemented, however, they require manually adding the animation object and the keyframe animation object requires you to get the lerper, so it's quite involved. I imagine the API would look something like this. build() would return the animation object, so you could specify completion callbacks, repeating, etc.

getSomeProperty_im().animateKeyframes(delay)
    .add(duration, easing, value)
    .jump(value)
    .hold(duration)
    .build()

[thecodewarrior]

Implemented in f116cba