ksysguardd: show Mandatory Access Control (SELinux/AppArmor) context

Summary:
Collect and display Mandatory Access Control (SELinux/AppArmor) context info from /proc/PID/attr/current.

Signed-off-by: Topi Miettinen <toiwoton@gmail.com>

Reviewers: davidedmundson

Reviewed By: davidedmundson

Subscribers: davidedmundson, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D20853