Show SNI when software renderer is in use

Summary: This then invokes the relevant KCM when clicked

Test Plan:
Forced software rendering, saw SNI
restarted, saw SNI
set "never show again". It hid itself
Restarted. It remained hidden

Reviewers: #plasma, broulik

Reviewed By: #plasma, broulik

Subscribers: alexeymin, broulik, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D12679