Add glTF + behave-graph.json examples.

[bhouston]

Some ideas:

• blink using lifecycle/start + delay + changing visibility - visibility only.
• an object that if you click it, it rotates to a random orientation - click + rotation.
• keyboard a/w/s/d that turns into translation of the object on screen - keyboard + translation.
• an object that if you click it, it begins rotating - click + interpolator.
• mouse over object and it get's larger until you leave the object and it returns to size - hover/enter/leave + scale.
• an object moves to a series of different locations (defined as nulls) and repeats - interpolators.

[bhouston]

I have the first example, changing visibility, coded up here: https://github.com/bhouston/behave-graph/pull/111

[oveddan]

Some unit tests to demonstrate this functionality would also be a great form of showing how to use this with gltfs.