Add some device properties which correspond to dehumidifiers

[graymalkin]

I have a "LEXENT MEVAGISSEY" dehumidifier (Amazon link), which uses a Gree-compatible controller. I found a couple of device properties which are not exposed in device.py which I've added and put appropriate accessors for. I'd like to add this so I can work on the Gree integration for home assistant and add dehumidifier support for Gree controlled dehumidifiers.

I do not know if other devices use this same protocol.

These are the properties I've added:

• Dwet: Target humidity (read-write, appears to be 15 + 5*value)
• DwatSen: Current humidity (read-only, integer)
• Dfltr: Clean air filter (read-only, boolean)
• DwatFul: Water tank full (read-only, boolean)
• Dmod: Dehumifier mode (read-only, on mine 0 = default, 9 = anion only) Oddly it's read-only, even though the mode can be toggled on the front-panel.

[cmroche]

LGTM.

[github-actions[bot]]

:tada: This PR is included in version 1.4.0 :tada:

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