Long term statistics support

Thanks to @FrnchFrgg , this version brings support for statistics!

type: custom:plotly-graph-dev
entities:
  - entity: sensor.temperature
    statistic: mean # min, mean, max or sum
    period: hour # 5minute, hour, day or month

This means that multi day plots can now be very snappy, and you can look way back in the past too.

Also, the API for attributes changed a bit: Instead of the old ugly climate.living::temperature hack, now it is:

type: custom:plotly-graph-dev
entities:
  - entity: climate.living
    attribute: temperature

(but the old api is kept too for backwards compatibility)

After we added statistics support, I decided to make a fairly big refactor to improve the API of both statistics and attributes.
Because of that, this one is marked as beta version. Please feel encouraged to report any bugs as issues, or drop a thanks to @FrnchFrgg in the discussions section if you were missing the feature!