Use Greek letters in OMEdit plots and diagrams

[max-privato]

Description

Steps to Reproduce

This is a follow-up of comment 16 in ticket #5447, where @adeas31 says:
I believe we should have a different ticket for it.

So here I replicate my comment from there:
Since Modelica is from its ground-up Unicode compliant, I think time has come to use greek letters when needed: greek-omega fo ohms, greek-mu for micro. I did this on my PlotXY, with Qt, and was straightforward.

This referred just to plots. Since this is a new ticket, I think it is better to add here also another place where greek-omega should be introduced: the unit of measure of resistors in diagrams (see enclosed picture). This feature has already been there in Dymola for some years, is good-looking, and spares space for the textual label, easing reading cluttered diagrams.

Version and OS

OM 1.18.0-dev233, Win10, 64 bit