(Re-)Add libreoffice-kde5 to task-kde-desktop
libreoffice-kde got removed from the kde-desktop task once (with e55a30c3) because it was not built anymore.
This changes with LibreOffice 6.1, where the gtk3 plugin disguised as a kde plugin + a kde5 native filepicker was added and results in a new libreoffice-kde5 package (with said libreoffice-kde as a transitional package). Amd LibreOffice 6.2 will get both KDE/Qt-native.
This is now in unstable, and I already prepared the re-addition of the LibreOffice KDE integration to tasksel.
Please merge :-)