Cleanup KPlotWidget

Cleanup KPlotWidget

KPlotWidget:

- added setAntialias(bool), set to true for smoother (but slower)
plots

- removed explicit double-buffering (Qt4 does this automatically)

- added top and right axes (by default, they show the same tickmarks
as bottom and left)

- added optional secondary data limits for showing alternate
set of tickmarks on top and right axes.

- removed setShowTickMarks() / setShowTickLabels()...each axis now
handles its own visibility logic.

KPlotAxis:

- each axis now calculates its own tickmark positions (rather
than KPlotWidget)

- rather than setting the number of tickmarks and distance between
them, the tickmark positions are now stored in a QList<double>

- simplified visibility logic:
  + isVisible() : draw axis and tickmarks ?
  + showTickLabels() : obvious
  + the axis label is drawn if it is not empty

- added new ticklabel format 't', which indicates that the ticklabel
values are decimal hours, and should be rendered with a clock-time
format ("hh:mm").  Other special format flags are possible.

I didn't have to modify kalzium or ktouch, so the API hasn't
changed too much.  Most of the changes are "under the hood".

I also didn't look at kmathtool, since they have their own copy
of KPlotWidget in the playground.  I'll let them decide if and when
to use this version.

CCMAIL: kde-edu@kde.org

svn path=/trunk/KDE/kdeedu/libkdeedu/; revision=581495