Set new icon for battery applet
Summary: It's not visible in the desktop system tray, but it is visible in the Plasma Mobile drawer where it is the only colorful icon. Let's use a monochrome one that actually looks like a battery instead
Reviewers: Plasma, bshah, broulik
Reviewed By: Plasma, broulik
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D24649