Power Monitor reliability fixes

This release fixes a few cases where the Power Monitor could get stuck or show no data.

Fixes

System Power Input now reads on desktop Macs. On a Mac mini, Studio, or Mac Pro the "System Power Input" figure sat at 0 and span on "Negotiating…" forever, because it was sourced from the battery controller, which desktops don't have. WhatCable now reads it from the System Management Controller instead, the same place the per-port readings come from. Big thanks to @jimmyorz for the Mac mini data and testing on #291.
Power Monitor no longer gets stuck on Macs powered through a display or dock. Thanks to @thomdekoning for the report (#296).
The version number in the app footer now links to that version's release notes on GitHub (#252).