Add Unit System Option For Fitbit

[bertbert72]

Description:

Allow overriding of the units to be used for the Fitbit sensor, e.g. allowing metric units to be used on an en_GB system.

Related issue (if applicable): fixes # n/a

Pull request in home-assistant.github.io with documentation (if applicable): home-assistant/home-assistant.io#4469

Example entry for configuration.yaml (if applicable):

sensor:
  - platform: fitbit
    clock_format: 12H
    unit_system: metric
    monitored_resources:
      - "body/weight"

Checklist:

• The code change is tested and works locally.

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.

If the code does not interact with devices:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass
• Tests have been added to verify that the new code works.

[houndci-bot]

line too long (83 > 79 characters)

[houndci-bot]

missing whitespace after ','

[fabaff]

This is already defined in const.py. Please import that.

[bertbert72]

Ok, done

[tinloaf]

It's somehow weird that en_US and en_GB are special. No other locale is handled specially… is that a limitation of the fitbit API? I couldn't find anything relating to that at https://python-fitbit.readthedocs.io/en/latest/ … In fact, they seem to be using en_UK instead of metric (see https://github.com/orcasgit/python-fitbit/blob/master/fitbit/api.py#L187 )

[bertbert72]

Yes, see here:

https://dev.fitbit.com/build/reference/web-api/basics/#units

Options are

en_US => US
en_GB => UK
none of the above or not provided => METRIC

So anything other than en_GB or en_US becomes metric. If they are using en_UK then that'll translate to metric in the API.

[tinloaf]

Okay, looking good! 👍

[balloob]

@tinloaf feel free to merge when you approve 👍