Add setting font options for axis

[Kvaz1r]

It should be possible to do:

        wxChartFontOptions fontOptions(wxFONTFAMILY_SWISS, 20, wxFONTSTYLE_NORMAL, wxFONTWEIGHT_BOLD, 0x666666);
        options->GetGridOptions().GetXAxisOptions().SetFontOptions(fontOptions);