Batch download data pose pickle

[carmichaelong]

Addresses #248

Adds pose pickles to download when using getMotionData() which is used by batchDownloadData.py.

Searching for uses of getMotionData() seems to indicate this should be a safe change. @antoinefalisse would you be able to review (should be a quick review) and indicate any worries of side effects from this?

[antoinefalisse]

@carmichaelong looking good. Would it make sense to make it optional?

[carmichaelong]

It could (for instance it would make sure that existing uses would not be affected), and happy to do that if you think it's helpful (either optional only on getMotionData() or also within batchDownloadData.py).

I figured if a user is downloading from this repository, it's likely this would be useful (and they get it from the web app download already too). Looks like it also doesn't increase download size too much (maybe less than 10%?)

[carmichaelong]

@antoinefalisse I finally circled back to this PR. added optional argument with default False to keep default behavior the same. Also adjusted the example to show that this is an option now. Should be a quick review.

[carmichaelong]

Thanks @antoinefalisse!