Option to set a minimal amount for untracked energy

[HenryLoenwind]

Energy measuring devices always differ in their precision. Chaining two will never give the exact same readout on both. It even gets worse when branching, i.e. one measuring the same thing as multiple others, due to rounding errors.

The result is that the energy dashboard is littered with "(untracked)" entries of 0.01 kWh, -0.01 kWh and so on. The maximum I see in my system (that's not actual use by a real untracked consumer) is 0.09 kWh on the hourly graph. (There's also one that shows +0.25 and -0.23 for the same device, but that's another issue.)

To get rid of that useless clutter, I propose a configurable (either globally or per device) threshold for listing untracked consumption. Ideally, it would be in "x% + y W", as with small consumptions, rounding errors are the main issue, which can be up to 100% per sub-device, whereas with large consumptions, measurement errors are the issue.