bnc#885825: Support borders around data labels.

(cherry picked from commit f1531cdaaebe706d909dc6ddde439ccb5f4ad36d)

Conflicts:
	chart2/inc/unonames.hxx
	chart2/source/model/main/DataPointProperties.cxx

Change-Id: Ib141413e523cbf73746876f727e9f80dda9f5f7c
Reviewed-on: https://gerrit.libreoffice.org/10561
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>
Tested-by: Markus Mohrhard <markus.mohrhard@googlemail.com>