D22315: Add setting to enable/disable text drag-and-drop (on by default)

[Thomas Schöps]

thomassc added a reviewer: KTextEditor.

REPOSITORY
  R39 KTextEditor

REVISION DETAIL
  https://phabricator.kde.org/D22315

To: thomassc, #ktexteditor
Cc: kwrite-devel, kde-frameworks-devel, LeGast00n, domson, michaelh, ngraham, 
bruns, demsking, cullmann, sars, dhaumann