Xiaomi Air Purifier: The name of the enum must be used here because of the speed_list

[syssi]

The fan.set_speed example value is lower-case and led to confusion. Both spellings are possible now: Idle & idle

Reverts: #12602

@balloob @OttoWinter Sorry for the mess. Could you merge this PR into the release branch?

[OttoWinter]

I can put it in the 0.64.0 milestone so that it isn't missed when releasing (please tell me if that's the correct way...)

Also: Just some thoughts, but this to me seems like just another case where enum is just incredibly weird in python (compared to other languages, like Java (😉)). Why do OperationMode() and OperationMode[] a) both exist and b) behave so differently? Also: [] apparently has almost double the speed of ()

[syssi]

This is the enum: https://github.com/rytilahti/python-miio/blob/master/miio/airpurifier.py#L15-L19

It's accessible in both ways. I'm using the enum to have a nice title at the dropdown:

The service must accept the title of the dropdown because I cannot populate the option value of the dropdown with other values.

[balloob]

Tagging the milestone is the right thing to do. I'll make sure to cherry-pick them before the release.