Summary:
* remove unneeded cmake includes
* consistently use org.kde.plasma.* prefix for names
* fix catalog names to match applet identifier
* bump min cmake version to 3.0
* remove duplicated X-KDE-PluginInfo-Name entries
* remove no longer (Plasma >=5.8) needed i18nd in wallpaper code
* prepare qml extension for ki18n usage
Reviewers: mart
Reviewed By: mart
Subscribers: kde-frameworks-devel, apol
Tags: #frameworks
Differential Revision: https://phabricator.kde.org/D10848
