[Kickoff] Draw FrameSvgItem behind kickoff configuration buttons

Summary:

This ensures we don't end up with a white icon (dark Plasma theme) on a light gray (default application colors) background. It also makes the configuration (draggable) buttons look more like a live preview.

similar to: https://phabricator.kde.org/D2884

Test Plan:
Breeze dark application scheme, Breeze dark Plasma theme
{F346143}
Breeze dark application scheme, Breeze light Plasma theme
{F346138}
Breeze light application scheme, Breeze light Plasma theme
{F346139}
Breeze light application scheme, Breeze dark Plasma theme
{F346142}

Reviewers: #plasma:_design, #plasma, davidedmundson

Reviewed By: #plasma, davidedmundson

Subscribers: davidedmundson, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D2900