Update Part2 to ModularSensors v0.25

I need to update Part 2 to work seamlessly with the latest version of ModularSensors, which is presently v0.24.1, but will likely be updated to v0.25.0 before we begin. The online tutorial was last updated in May 2019 for v0.21.3, and the changes are substantial.

See https://github.com/EnviroDIY/ModularSensors/releases 