
plot_var(q,xp,t)
  change to be plot_var(data)  similar to afterx for more flexibility.

change data to current_data in afterx, plot_var for clarity

return current_data from plotframe and plotitemN and add as attribute of
Iplotclaw so that user has easy access to current_data interactively.

Change ClawPlotItem attributes 'contour_nlevels' etc to 'nlevels' etc.
with same names as kwargs of contour command.  Modify _set and _get methods
of ClawPlotItem to store attributes that are also kwargs into kwargs
dictionary that is passed to plot command.

add plotter attribute to ClawPlotFigure for 'visit' or 'mayavi' options.

