make snapsat-worker pip-installable

[jqtrde]

Packaging is still a bit of a mystery to me. I'd like to get this thing in a state where we can pip install landsat-worker, and know that what's pulled down is testable and works as intended.

Lots of (sometimes conflicting) resources out there, but this is definitely going to require some trial and error:

• Packaging and distributing projects
• How to package your Python code
• Tool recommendations for packaging
• Declaring dependencies in setup.py vs requirements.txt

😰