Many plots missing _render_icon method

[corranwebster]

Problem Description

A number of plot renderer subclasses are missing the _render_icon method that is used to draw icons in the legend. This includes many of the 1D plots, but also many of the others.

There should be an audit of the various classes, and where feasible a missing method written.

In many cases the method may be copyable from similar classes.

[aaronayres35]

ref: #508