Added support for adafruit EMC2101

[JeremyLaurenson]

Added temperature sensor support for Adafruit 2101
Added output support to change fan speed on Adafruit 2101

[Vaarlion]

have you try setting up the clock to match the requirement of 25Khz for some fan ?

https://4donline.ihs.com/images/VipMasterIC/IC/SMSC/SMSCS00913/SMSCS00913-1.pdf

[Vaarlion]

sadly, this wasn't a working branch for me, i've done a lot of tweak to bring it to a working state but i haven't tested everything yet.
You can find this work here for now: https://github.com/Vaarlion/OctoPrint-Enclosure/commits/master
I'll try to think to edit that link when i move all commit to a branch.

One thing that i don't quite understand about the pwm temperature logic is that it seam to override all other logic
No "off when not printing, on when printing, and keep on after for a while to cool down" for example.
Maybe I've missed something but for me this lake some "warm up the enclosure" and "cool down the enclosure" step.

I also have a huge doubt with this one : Vaarlion@234be72
It seam to me that some control of PWM output never did anything more than write the wanted duty cycle to the output state, without actually changing the pin duty cycle ?