Now that linked services are possible: add filter maintenance support

[gjvanderheiden]

Filter Maintenance isn't supported yet. Played around with the Apple HomeKit Accessory Simulator and found out that it only works as a linked service. An Air Purifier can have it as a linked service, also mentioned in the HAP spec from Apple.

Using it as a separate service doesn't work, not in the Home app that is. Eve works better and also supports a Filter Maintenance service as a separate service (e.g. not linked to an Air Purifier service).

Then there is an other peculiar issue with homekit: The Home app doesn't support reset filter. Tried it with the Apple HomeKit Accessory Simulator and with a modified version of HAP-Java. Only Eve supports it. But that is an issue on the Apple Home app.

Anyways, wanted to make an issue to mark I'm working on this and a PR will follow.

[yfre]

@gjvanderheiden thanks for opening it. i also started to implement filter for the same reasons - with linked service it makes sense now
at which stage you are? i have created all filter characteristics but not the service yet, which probably another 2-3 hours with testing.

if you are almost ready i will stop and wait for your PR, otherwise i will finish and commit today/tomorrow my PR.

[gjvanderheiden]

I've got it working. I also fixed a little issue on the AirPurifier, it didn't support rotation speed

[gjvanderheiden]

pr #124