Add Alphasense CO2 Sensors; Redirect ADS1X15 dependency to Adafruit

[aufdenkampe]

This PR is primarily to add the Alphasense IRC-A1 Nondispersive Infrared (NDIR) Carbon Dioxide (CO2) sensor to the list of supported sensors.

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It also paves the way for other Alphasense gas sensors to be implemented.

Last, bundled into this PR is a code fix to support the following change in the dependency for the Mayfly's Analog-to-Digital Converter (ADC):

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  There are many compelling reasons to switch this core dependency, as described in the issue.

This PR is not yet 100% ready, as some testing is first required to confirm that everything is working on sensors that use the ADS1X15. I also need to complete documentation for the Alphasense sensor, primarily via adding a block to the menu-a-la-carte.ino example.

This PR begins such review.

[aufdenkampe]

@bellahenkel, can you confirm that the Alphasense CO2 sensor is working using this sketch: https://github.com/bellahenkel/Soil-Sensing-Device/tree/triple_logger/examples/AlphasenseCO2_simple_logging

[bellahenkel]

@aufdenkampe Everything appears to be working on my end!

[aufdenkampe]

@SRGDamia1, is this something you might be able to review and merge sooner than later?

I think this feature branch adds important new capabilities and ease-of-use benefits (i.e. all recent tutorials use Adafruit's v2 for ADS1X15) that are outlined in:

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