Add new humidifier entity integration

[Shulyaka]

Description:

As per discussion in home-assistant/architecture#288, this is the pull request to add an integration for humidifier and dehumidifier devices, which are the consumer devices whose main purpose is to add or remove moisture from the air.
Once this PR is reviewed and merged, I will also raise separate pull requests for generic_hygrostat platform and for the humidity devices support in demo, emulated_hue, prometheus, homekit. and google_assistant integrations. However if you prefer I can combine it all in one PR.

Related issue (if applicable): N/A
Pull request with documentation for home-assistant.io (if applicable): home-assistant/home-assistant.io#11151
Pull request with documentation for developers.home-assistant.io: home-assistant/developers.home-assistant#356
Architecture issue: home-assistant/architecture#310

Example entry for configuration.yaml (if applicable):

humidifier:
  - platform: humidifier_platform_1
    name: Hygrostat Zone 1
    ...
  - platform: humidifier_platform_2
    name: Humidifier Bedroom
    ...

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in home-assistant.io

If the code communicates with devices, web services, or third-party tools:

• The manifest file has all fields filled out correctly. Update and include derived files by running python3 -m script.hassfest.
• New or updated dependencies have been added to requirements_all.txt by running python3 -m script.gen_requirements_all.
• Untested files have been added to .coveragerc.

If the code does not interact with devices:

• Tests have been added to verify that the new code works.

[probot-home-assistant]

Hey there @home-assistant/core, mind taking a look at this pull request as its been labeled with a integration (history) you are listed as a codeowner for? Thanks!

[Shulyaka]

Looking into #28690 I realized that I also need to add support for the fan. Will do probably today or tomorrow.

[Shulyaka]

Rebased in an attempt to fix CI checks...

[fabaff]

It requires a demo platform in addition.

[Shulyaka]

@fabaff Done.

[Shulyaka]

I don't know how I removed review request from @home-assistant/core and how to add "integration: demo" label to this issue

[Shulyaka]

I haven't started on frontend part yet (was waiting for this PR to be merged first), but if you think it is almost ready to be merged, I will start now. If anyone has his own plans for the frontend, please let me know.

[Shulyaka]

The frontend part is ready from my perspective.

[balloob]

🎉 🎉 🎉

Will do a frontend release tomorrow that includes humidifier support.

[dshanske]

Can't wait till winter...