Provide option to change stress legend number format

[robbievanleeuwen]

Discussed in #279

^{Originally posted by Chivos June 12, 2023}
Hi,
How can I change the format number of the stress scale when plotting the results ?
The idea is to format in float with only 1 or 2 decimals, which seems enough for stresses in steel sections when expressed in MPa.
I'am not used with python and matplotlib, and I can't found how.

[robbievanleeuwen]

Further improvements:

• Add colour limits option e.g. only plot stresses when they exceed or are below a threshold.
• Add option to change mesh opacity for all plot types.
• Plot stress on only certain material groups