#826 axis color control

[Jeremy Faden]

A few people have asked for the ability to set the axis color. I've been reluctant to add too many controls, but since I plan on adding custom editors for all the Das2 components, I think it's okay.

[Jeremy Faden]

A reminder of the changes needed:

1. add the property
2. syncTo copies the property
3. diffs identifies the property change
4. AxisController.bind the property to the DasAxis
5. AxisController.syncTo copies the property
6. ApplicationController.reset resets the property

[Jeremy Faden]

I also added the axisOffset feature, which is very similar and would be used in conjunction with the foreground property.

[Jeremy Faden]

There's an annoying bug now, that the default color is black so if you load a black-background .vap the axes are not drawn properly.

[Jeremy Faden]

I've dealt with the back backgrounds, but there are also white background images with grey foreground which now come up black.

[Jeremy Faden]

This demos:

dom.plots[0].yaxis.controller.dasAxis.foreground= Color.RED
dom.plots[0].yaxis.controller.dasAxis.axisOffset= '1em'

[Jeremy Faden]

Actually this is probably pending. I see now looking at the code this was intended for the .vap and a property above the controller, and this was backed out. No one has asked for this again, so I will leave it closed for now.