[batterymonitor] Port Battery and Brightness settings to QQC2 and Kirigami

Test Plan:
Before
{F6633708}
After
{F6633709}

Reviewers: #vdg, #plasma, ngraham

Reviewed By: #vdg, ngraham

Subscribers: ngraham, filipf, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D19295