Add support for "used energy"

[tkilla77]

See issue #45.

This is just a preliminary request to start the discussion before I start investing... - would you be open for a real request?

What kind of code quality & test coverage do you require?

Missing: Translations other than German
Missing: Tests

[hansmi]

What kind of code quality & test coverage do you require?

Looks good as a draft. Can you please cover the new code in collector_test.go:TestCollectWebSocketParts?

To get the non-German strings I'd recommend switching the controller to the respective language. There's also wp2reg-language-extractor, but it only works if the software version uses the external files. At some point they switched to embedding the strings in the binary, making them harder to extract (see also #37). I didn't update the tool accordingly.

[hansmi]

@tkilla77, do you plan to keep working on this feature?

[tkilla77]

@tkilla77, do you plan to keep working on this feature?

Sorry for the long delay... unlikely I will find time in the next three weeks to work on this. Feel free to close.

[hansmi]

Please re-open this PR when you had time to work on it again.