add [a] AP list implementation for M0 wifi

[jakehlee]

Only the WICED wifi sensors had the ability to list access points.
We've added this menu option for M0 wifi sensors as well, as it's a useful feature for our chrome extension setup project.
We used the official adafruit tutorial as reference. We can also confirm that this works on our Heat Seek M0 sensor.

• CSEG Tech

[bolandrm]

This looks good overall. At the moment, it isn't practical to update all of the sensors with new firmware. We can consider doing this in the future, but for now the chrome extension will need to gracefully handle the case where the access point listing is not available.

[jakehlee]

Yes, Noelle also mentioned that during our meeting. The extension will check if an [a] option is available and handle it accordingly. Meanwhile, this PR can wait until the next heat season :)