add percentage (DPT_Scaling) KNX sensors

[tiktok7]

1. moved basic functionality to KNXSensorBaseClass instead of
   KNXSensorFloatClass
2. all derived classes just override the "convert" method to handle different data formats
3. added "if" clause in setup for a "percentage" sensor type and added KNXSensorDPTScalingClass with DPT_Scaling conversion (raw: 0 - 255 = display: 0 - 100)

Description:

This change is intended to provide support for additional data items on devices such as thermostats/covers that use the scaled percentage data format (1 byte). The existing sensors use the 2 byte float data format.

Related issue (if applicable): fixes #

Pull request in home-assistant.github.io with documentation (if applicable): home-assistant/home-assistant.io#2876

Example entry for configuration.yaml (if applicable):

 - platform: knx
   name: percent
   type: percentage
   address: 1/0/5

Checklist:

Note: there are no new dependencies and no new files

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

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

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

• 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.

[mention-bot]

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

[ghost]

👍

[balloob]

Please add a PLATFORM_SCHEMA based on voluptuous that validates CONF_TYPE is one of the approved values.

Example from KNX light: https://github.com/home-assistant/home-assistant/blob/dev/homeassistant/components/light/knx.py#L20-L24

[tiktok7]

No problem. Thanks for the quick feedback.

[tiktok7]

@balloob : that's the best I could do

[balloob]

Thanks!

[tiktok7]

@daBONDi @Julius2342 @open-homeautomation : I should have thought of asking earlier but you three seem to have made the biggest changes on the knx platform to date. I had to make a larger than expected change to this PR to add in a PLATFORM_SCHEMA so it may have side-effects on other knx sensors but don't have enough devices to test all types. Do you think you could check your devices for any issues for the lux/speed/temp sensors on the latest dev branch?

[ghost]

Temp sensors here are working fine. I don't have any Lux/speed sensors, but I would not expect problems.