Make cutoff point for Scientific and Engineering notation customizable

[DanielNoord]

Building on the discussion in #282 we should make the cut-off point where Scientific and Engineering notation start customizable by the user.
With #371 I have set this cut-off at 999999, but this should become a user-setting.

Ideally we would:

• Add a variable that stores user preference about cut-off point
• Change CM.Disp.Beautify to use that variable
• A new line in the options menu that appears when scale is set to Scientific or Engineering and that allows changing of the variable