Avg price for tibber sensor

[Danielhiversen]

Description:

Avg price for tibber sensor

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.

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

• New dependencies have been added to the REQUIREMENTS variable ([example][ex-requir]).
• New dependencies are only imported inside functions that use them ([example][ex-import]).
• New or updated dependencies have been added to requirements_all.txt by running script/gen_requirements_all.py.
• New files were added to .coveragerc.

[MartinHjelmare]

Looks good!

[hulkhaugen]

Is it possible to round down to only 3 decimals without setting up a template sensor?

[Danielhiversen]

I can add a round to the code.