Added a unit test for testing that text decorations are exported
correctly.

Change-Id: I2bd71974242a0007726fbdd5ef5637a9ec62fd47
Reviewed-on: https://gerrit.libreoffice.org/19870Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Andras Timar <andras.timar@collabora.com>