Fix installation path of dataengine

KPluginLoader looks into subdirs based on the servicetype, so this
commit is needed to make it load.

Reviewed-by:Sven Brauch
Compile fix for MSVC

Multi-line strings in QStringLiteral don't work on MSVC.
Just removing the QStringLiteral() here, this is not performance
critical anyway.
Make KF5Runner optional

This is useful for Windows, where one can build KDevelop without the Plasma/Runner dependency