bnc#882627: Allow to edit spacing to contents even with no borders visible.

SfxItemSet::MergeValue changes some items from SFX_ITEM_DEFAULT state to
SFX_ITEM_SET which I think is a bug but this patch avoids the problem too.
The issue was: visible changes in some tables, after changing e.g.
borders spacing, because the cells had wrong SfxItemSet after the process.

(cherry picked from commit b1d8df61b47e84bf0de64342556049673dd9c543)
Signed-off-by: Andras Timar <andras.timar@collabora.com>

Conflicts:
	cui/source/dialogs/sdrcelldlg.cxx
	cui/source/inc/border.hxx
	cui/source/inc/sdrcelldlg.hxx
	cui/source/tabpages/border.cxx
	svx/source/table/tablecontroller.cxx

Change-Id: I676b211e1a4a1d7341c385d63503aa740718ed5d