improve control over plotting

• Give the user more control about which curves to plot. Default to the two final curves and add an argument controlling wether the toxicant and tox+env curves should be drawn. Keep the argument for the simple models. So there will be three booleans for three pairs of curves.
• Also accept the ... argument for more fine control of axes, colors, pty, etc. Remember to use hasArg().
• The axes look bad when saving the plots with type = "cairo". This comes from anti-aliasing when overlaying multiple lines.

changed milestone to %v2.0

added enhancement label

removed milestone

mentioned in issue #21 (closed)

The point with the ... argument will not happen for the forseeable future. If users want to customize the plotting further they will have to write their own plot code. But I plan to explain how the plotting works in more detail so that will become easier (see #24 (closed)). plot_effect() and plot_stress() are just there to get a quick look of the model in the style of the plots from the paper.

changed the description

mentioned in commit e7630786

mentioned in commit c074b343

closed via merge request !19 (merged)

mentioned in commit 7006144a