Fix two recent regressions on the graphics sub-dialog

[rdstern]

@N-thony I suggest these are both easy to fix and could be by anyone? It may be worth a bit of detective work, at the same time, to see how they have arisen, in case there are more that we have yet to uncover.

a) This one seems to do no harm. It has come after Version 0.7.15. It has added 2 lines of exta text, namely 2 digit after the first factor and a long text after the second! Why has this happened and where have they come from?

b) The legend, see below:

This is a problem. The default used to be None and this has disappeared. This was a problem I didn't notice in 0.7.14 and 15, but I think was ok before.

c) I don't know if this is related to b) In the pair-plot option, see below, I thought the pair-plot options were now enabled. They may be linked to the legend problem above? Maybe they get enabled later when using the dialog? This was pull request #8005 and it mentioned the legend.

[lloyddewit]

@rdstern @derekagorhom
For part b) above, the None option was deliberately removed in PR #8316. Was this correct?

[derekagorhom]

@lloyddewit
Roger requested that change in issue #8288
see here

I think it can be added back again