add battery widget to all skins

[Be]

The C++ was taken care of with https://github.com/mixxxdj/mixxx/pull/401 . Let's add the widget to skins.

[jus (jus)]

+1
But Users won´t see it until compiled with ``battery=1`` option, which is disabled by default, and in the official builds.

This (+ the icons in the attachment) is what i use in my personal branch.
<Battery>
   <MaximumSize><Variable name="SquareButtonMaximumSize"/></MaximumSize>
   <PixmapUnknown scalemode="TILE">ic_battery_unknown_48px.svg</PixmapUnknown>
   <PixmapCharged scalemode="TILE">ic_battery_charged_48px.svg</PixmapCharged>
   <NumberStates>1</NumberStates>
   <PixmapsCharging scalemode="TILE">ic_battery_charging_%1_48px.svg</PixmapsCharging>
   <PixmapsDischarging scalemode="TILE">ic_battery_discharging_%1_48px.svg</PixmapsDischarging>
</Battery>

[jus (jus)]

BTW Apple decides to remove the battery indicator from the Finder´s toolbar for macOS Sierra 10.12.2 [1].
Would be nice to have some feedback from users on 10.12.2+ if the widget in Mixxx still works.

[1] https://www.macrumors.com/2016/12/13/macos-sierra-10-12-2-battery-life-indicator/

[ghomem (gustavo)]

+1 on this.

I'm using a 10" device that boots directly into fullscreen Mixxx and therefore it is not possible to see the battery state, neither if the device is being charged. This is risky :-)

A battery indicator directly on Mixxx would be a great thing.

[ronso0 (ronso0)]

Deere:
https://github.com/mixxxdj/mixxx/pull/2161

[Swiftb0y (swiftb0y)]

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/8792