[Lock, login & logout screen] Add visual feedback to action buttons when pressed
Summary: The action buttons were missing a visual indication of when they were being pressed so this patch adds it by drawing another an animated rectangle when the button is pressed.
Test Plan:
Reviewers: VDG, Plasma, ngraham, davidedmundson
Reviewed By: VDG, Plasma, ngraham, davidedmundson
Subscribers: broulik, abetts, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D21062