* added new command .uno:Watermark
* if no arguments are provided the dialog
  is opened where user can enter the text
* with provided Text argument the watermark
  is created
* created SfxWatermarkItem to transfer
  watermark properties
* dialog loads current setings
* SetClassification use SetWatermark

Change-Id: Ifc1319f5aa7c11bb141f8e4b5b9a5088613021c2
Reviewed-on: https://gerrit.libreoffice.org/37599Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Szymon Kłos <szymon.klos@collabora.com>