Robust Transition Plugin for transition animations

[rphumulock]

When working on #124 the more time I spent on it, the more it seems like the best approach would be to develop a fully comprehensive transition plugin. I had come up with a solution to the issue but it would likely become problematic in the long run and doesn't seem like the right direction.

Speaking with @delaneyj we both agree this is probably the best solution moving forward.

This could be utilizing modern CSS techniques or tweeing. Jotting some ideas down here for the future, something like:

data-tween-opacity.cascade

[bencroker]

The data-show attribute has been simplified to only add/remove style="display: none". For anything custom, including transitions, we now have the data-class attribute.