lib.plot: Remove deprecated getters and setter functions (they've been replaced by properties)

[dougthor42]

(This issue was created because PR #117 could not be finished in its entirety)

Many of the getters and setters in lib.plot have been deprecated and replaced with properties.

The old getters and setters can be removed when the deprecation period is complete (determed
by pkg maintainers).

Examples:

• SetXSpec, GetXSpec --> XSpec property
• SetFontSizeAxis, GetFontSizeAxis --> fontSizeAxis property.

Removing these deprecated items will significantly reduce the LoC in lib.plot.plotcanvas and will make maintaining the plot package much easier.

[mesalu]

@RobinD42 When do you think would be a good release for removing the deprecated methods? 4.1?

[RobinD42]

Yes, probably sometime in the 4.1 series, but maybe not right away to give people a chance to make any needed changes in their code.