AirDogX3, AirDogX5, AirDogX7SM support

[alexeypetrenko]

This is a PR following this discussion #72

I tried to follow existing structure as close as possilbe.

I inherited a new object from XiaomiGenericDevice and not from XiaomiAirPurifier. It seems that there are a lot of unneeded functionality in XiaomiAirPurifier. Although, I had to copy async_update as is. Hope it is not a problem

Unlike other devices, this device uses a combination of mode and speed to set any given preset.
So, there is no ready made _preset_modes list.
I mapped usable combinations to _preset_modes using _preset_modes_to_mode_speed dictionary.

To function this PR requires following bug-fix in python-miio to be accepted: rytilahti/python-miio#993

I tested it on both of my devices (#72 (comment)).
Everything works fine.

Service xiaomi_miio_airpurifier: fan_set_filters_cleaned also works.

[syssi]

Good job! Can be merged as soon the next python-miio version is released.