To make the pressure data dynamic (size of the arrays depending
on the cylinders in the dive), it has to be separated from the
standard plot_data structure. To enable this, use indexes instead
of pointers to plot_data elements. This commit converts
the RulerItem2 to use an index.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
fbd74c26d6