In the future we want to use our own axis implementation to
convert from/to screen coordinates. For this purpose, we
need to save the axes with the series. Especially if we want
to support multiple series on different axes.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
Add a interface class for the chart series used by the statistics
module. Abstract virtual functions are declared for replotting
and selecting items.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>