Add video wrappers using chain loading

Fixes #12 (closed)

@tiago.pereira using this and bob.bio.base!155 (merged) I can run

bin/bob bio baseline idiap_casia_inception_v2_centerloss_rgb swan-video video-wrapper

and it works magically!

mentioned in merge request bob.bio.base!155 (merged)

I will merge this one.

Works like a charm

Thanks

mentioned in commit 8d91155f

merged

Why do you print these error messages? Shouldn't we use logger.error instead?

When you re-raise the exception here, I think you will lose the error back-trace. Just call raise (without e) here.