D8850: Support drag and drop between shared folder view containments

[Eike Hein]

hein accepted this revision.

REVISION DETAIL
  https://phabricator.kde.org/D8850

To: amantia, mwolff, #plasma, hein
Cc: broulik, plasma-devel, ZrenBot, progwolff, lesliezhai, ali-mohamed, 
jensreuterberg, abetts, sebas, apol, mart