Export:
* Watermarks saved using Writer were very small in the MSO.
  Export fUsegtextFStretch property in the Geometry Text
  Boolean Properties.
* tdf#91687: SnapRect contains size of Watermark after rotation.
  We have to export size without rotation.

Import:
* When import set height depending on used font and width.
  Text will keep the ratio. Remember the padding for export.

* added unit test
* introduced enum to avoid magic numbers for stretch and best fit
  properties.

Change-Id: I3427afe78488d499f13c543ca401c096161aaf34
Reviewed-on: https://gerrit.libreoffice.org/38979Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Andras Timar <andras.timar@collabora.com>