In combined charts, now X category axis crosses the Y axis at the right
place, all data series are attached to the right Y axis, and the
Y major grid isn't lost.

Note: Let's check which axis is attached to the first charttype
(in case of combined chart, the first one is a column chart) and create
that axis first. In OOXML standard, the first CT_valAx tag contains the
axID of the primary axis and the second CT_valAx tag contains the axID
of the secondary axis. 


Change-Id: Ib123f95ec41ef5dbbf0599efd7a646f4640a9b70
Reviewed-on: https://gerrit.libreoffice.org/70464Reviewed-by: László Németh <nemeth@numbertext.org>
Tested-by: László Németh <nemeth@numbertext.org>