Finished the port of the plot_profile code.

There are a few regressions, mostly because the text
is not being plotted yet and the background of some
of the curves are not being applied.
This is because QGrapdien is based on the coordinates
of the items that I wanna paint, but I'v setted a
QGradient that's global and doesn't take this into
consideration.

all curves are being plotted. in Small resolutions
they plot bad. but it's just a matter of redrawing
in the correct resolution.

the Line widths are being hardcoded now, on the cairo
version they weren't, this will need a bit of porting
too.

Signed-off-by: Tomaz Canabrava <tcanabrava@kde.org>