[software/co2] Add support for reading GPS over I2C

[abesto]

(Fixes #91)

Watch out, this sits on top of #92. I only meaningfully tested the two of them together, but it kinda makes sense to at least think about them separately, as they're both fairly big and do different things. You may want to look at just the diff on top of #92.

• Refactor co2.py to allow multiple GPS provider implementations
• Add a GPS implementation using I2C (tested)
• Add a dummy GPS implementation (tested)
• Keep the GPSD implementation (NOT tested)
• Sets up the logging module and uses it for all output (Timestamps Are Good (TM))

[keenanjohnson]

@all-contributors please add @abesto for his incredibly great and thoughtful code contributions.

[allcontributors[bot]]

@keenanjohnson

I've put up a pull request to add @abesto! :tada:

[keenanjohnson]

This looks good to me! I deployed to another raspberry pi 4 cm to confirm that everything still works with the GPSD original stuff.

Thanks so much for the changeset!