those changes make getting/setting of text background colour
possible from toolbar and sidebar buttons, but likely more
handlers needs to be added to various other places in the code

Change-Id: I698ca2304399befdd63317eb8872aa3129f27637
Reviewed-on: https://gerrit.libreoffice.org/15909Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Yousuf Philips <philipz85@hotmail.com>