Templates: consistent naming, fix translation catalog names & more
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