Refactor the various Plot classes

[MatthewWhiting]

Several improvements:

• Use inheritance to better associate the classes
• Split into different files, one for each class (hard to follow currently)
  • Perhaps in a new directory?
• Inheritance will simplify the code, removing repeated stuff.

[MatthewWhiting]

Have two functions in plotting.cc called drawSpectralRange - one which takes a SpectralPlot? object, and one taking a SimpleSpectralPlot? object.

These should be unified by making use of the inheritance, and really put within the class to act as frontends to the drawVelRange function.

[MatthewWhiting]

Not clear what should happen to void plotWCSaxes(struct wcsprm *wcs, size_t *axes, int textColour, int axisColour)

Would it be better to put this in Utils, as it is a reasonably generic front-end to cpgsbox that doesn't require any of the other Duchamp classes.

Perhaps a new file Utils/PlottingUtilities?.cc?

[MatthewWhiting]

Here's a possible arrangement:

• DuchampPlot - base class, handles size of page & identifier
  • ImagePlot - largely as it is, devolving basic stuff to DuchampPlot
  • MultipleDuchampPlot - base class for plots with multiple entries on a page
    • CutoutPlot - largely as is.
    • SpectralPlot - largely as is
      • SimpleSpectralPlot - while this isn't strictly a multiple plot, it is basically the spectralPlot but with different bounds for the main plot and a different label function. Most of the underlying stuff is the same though. It also requires access to similar functions (such as the flagged channel marking).

[MatthewWhiting]

Done in [1241], [1242] and [1250]. Have refactored according to the description above, and moved plotWCSaxes as described (although renamed to wcsAxes).

Builds fine.

Closing ticket.