Polar 1D bugs/oversights

[chaosphere2112]

• The list function on Polar1D just provides the vcsaddons default attributes.
• You can't pass multiple slabs to x.plot(polar1d) (need to update the n_slabs attribute)
• plot returns the canvas. It should probably return either a) a list of display plots, or b) a display plot with enough metadata to remove or redraw the entire plot.
• The box1 line drawn around the plot is being drawn on top of by the last layer of ytic1

[doutriaux1]

@chaosphere2112 just checking this is still TODO right?

[chaosphere2112]

Probably. You can check the n_slabs property on a polar oned to make sure.