Fix handling of color for labels

[stefangachter]

According to the description, the color for origin and axis labels should default to color. However,

• if origin color is defined without a frame label, then origin color is ignored
• if a frame label is given, then the color is set to blue for origin and axis labels

X = SE3.Rand()
X.plot(color=["r","g","b"], textcolor="k", origincolor="k", style="line")

X.plot(frame="A", color=["r","g","b"], textcolor="k", origincolor="k", style="line")

There was some "code duplication".

[stefangachter]

Note, this fix is slightly different from #58 and #67. It considers color of origin as well.

[petercorke]

will this resolve the issues with #67 and #69 as well? This might as well all go out in 1.1.6 soon, am keen to push the r2q fix.

[stefangachter]

Yes, this will fix #67 but not #69. #69 is a different issue.