Move file caching outside of the vizier project directory

[okennedy]

What pain point is this feature intended to address? Please describe.

• Vizier imports data files into the vizier project directories. This makes vizier project directories ginormous --- hard to upload to GIT, hard to use in a variety of situations.
• Files needed by multiple projects

Describe the solution you'd like @julianafreire suggests https://www.fatiando.org/pooch/latest/ , which provides file management using a local cache repository, disconnected from any specific project folder. It also has some nice features like checksumming.

• Integrate first-class support for pooch
• Mimic the pooch API / allow access to pooch cache folders
• Implement something analogous in vizier.

Describe alternatives you've considered Ginormous vizier.db folders