Rewrite autoplot() methods to use the special scales

[aphalo]

Because of historical reasons, the autoplot() methods define axis labels without using the scales defined in 'ggspectra' making them less flexible and a bit inconsistent. These methods could be updated to use the scales and at the same time add support for enabling and disabling symbols in axis labels as per #8 .

[aphalo]

'ggplot2' most likely will soon support data dictionaries. This will help with axis and other guide labels. 'gguidance' may also add useful functions.