d.correlate: add plotting of axes

[neteler]

At time d.correlate does not plot the axes (with some ticks and the variable names). Example:

https://grass.osgeo.org/grass72/manuals/d_correlate_plot.png

This would be quite helpful to have...

[neteler]

Suggestion for a start:

Since ticks may be complicated, for now it would be helpful to see which axes is x and which is y (not quite obvious from the current graph)

[mlennert]

I think we should decide on whether we want to continue to invest in d.correlate, or whether the scatterplot tool currently integrated into the Map Display (although it does not work for me: #3112) should be made also into a standalone g.gui.scatterplot tool which would then offer more layouting functionality than d.correlate.

[neteler]

Replying to mlennert:

... a standalone g.gui.scatterplot tool which would then offer more layouting functionality than d.correlate.

Big +1, no need to further develop d.correlate at this point. Seems I forgot about it due to the current absence of a g.gui.scatterplot start script :)

I'll create a new ticket (#3113) and close this ticket.