Revert "Revert "Get rid of KDELibs4Support""

Summary:
This reverts commit 55603160.

"Get rid of KDELibs4Support" was reverted because Can* methods
of PowerManagement class returned incorrect values due to async
DBus calls. Use blocking DBus calls now.

Reviewers: davidedmundson, broulik, #plasma

Reviewed By: davidedmundson, #plasma

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D11744