Add CZML and DynamicScene support for the Stripe material.

Title says it all.  One thing we may want to consider doing (and I can do it as part of this PR if desired) is renaming the stripe properties to better names.  `lightColor`/`darkColor` doesn't really make sense, maybe `firstColor`, `secondColor`?  I didn't want to rename things willy-nilly until hearing from you guys and the uniforms and DataSource layers should definitely match.

Also, the `horizontal` is a bit of a boolean trap, but I wasn't sure what we wanted to do there.  We can keep it as is at the uniform level (since I imagine it has to be that way) and introduce an enum at the DynamicScene and CZML layers.  Thoughts?

Finally, I added `testDefinitionChanged` which can now be used to simplify a lot of the other property specs, I'll do that in another pull request.