Allow users to control autoplay feature on Python animation frames

Hey all,

Loving the new animation functionality you've introduced!

It would be great if you could allow us to decide whether or not we want the animation to autoplay. 

For example, your GapMinder plot created with the Python API [here](https://plot.ly/python/animations/) autoplays, whilst the same plot with .js [here](https://plot.ly/javascript/animations/) doesn't.

Cheers!