add knx cover support

[tiktok7]

Adds support for KNX covers (roller shutters, window blinds)

Description:

Related feature request: https://community.home-assistant.io/t/support-for-knx-shutters-position-stop/14142

Notes

1. Tested with MDT roller shutter. This hardware uses 0 as open and 100 as closed, which is the opposite of the base cover implementation. This problem is mentioned here, which appeared to suggest that the polymer frontend would automatically reverse the definition of open/closed based on the device class so I also added optional support for the "device_class" setting. When I tested that locally it did not appear to work (although the icon did change)

2. The KNXMultiAddressDevice storage of address names was also changed from class storage to object instance storage because the same address names are used for object instance so the values were being overwritten.

3. Needed to add calls supporting percentage type DPT_Scaling used for KNX position values in cover devices

Pull request in home-assistant.github.io with documentation (if applicable): home-assistant/home-assistant.io#2845

Example entry for configuration.yaml (if applicable):

cover:
  - platform: knx
    updown_address: 9/0/0
    stop_address: 9/0/1
    setposition_address: 9/0/3
    getposition_address: 9/0/4

Checklist:

Note: no new dependencies, tests pass. Lint and pydoc warnings from tox have been corrected in the updated files

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

• Documentation added/updated in home-assistant.github.io

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass

• New dependencies have been added to the REQUIREMENTS variable (example).

• New dependencies are only imported inside functions that use them (example).

• New dependencies have been added to requirements_all.txt by running script/gen_requirements_all.py.

• New files were added to .coveragerc.

[homeassistant]

Hi @tiktok7,

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Once you do that we will be able to review and accept this pull request.

Thanks!

[mention-bot]

@tiktok7, thanks for your PR! By analyzing the history of the files in this pull request, we identified @fabaff, @balloob and @pvizeli to be potential reviewers.

[tiktok7]

It's my first time to make a PR for the project. If I need to do something else to get this change considered for review/merging could someone give me a hint?

[balloob]

This is awesome. Looks all great 🐬 🎉

I removed the property device_class that you added to the cover entity, as it's already party of the entity base class.