Deprecate CopyCat due to age and size and unavailability

[cleong110]

#91 must be merged first.

Deprecation:

• Unavailable: https://wearables.cc.gatech.edu/projects/copycat/# shows no method to download the dataset.
• Small (420 phrases)
• Not commonly used/relevant.

Features:
https://ieeexplore.ieee.org/document/5543268 describes 420 phrases with glosses, accelerometer data, video.

[AmitMY]

Approved and merged, but comment I was thinking on:
perhaps we should include a field under each dataset: which papers are using it
such that it would be easier to note an unused dataset etc

[cleong110]

Hmmm that's an interesting idea, I'll make an issue. I wonder if we could do it automatically somehow?