Preparing for dark mode.

[CEXT-Dan]

See [#454]

wxWidgets has a settings class I can override to do limited fine tuning with theming. My original thought was to theme all the controls to match CAdUiThemeManager, due to constraints, I can mostly only do wxWindow, wxPanel backgrounds.

I think it looks pretty good, IMHO, so I added it as default, but I’m on the fence if this should be the case

AutoCAD uses COLORTHEME sysvar to determine dark mode.

I plan on adding env

• PYRX_COLORTHEME, “0” = don’t use dark mode regardless of COLORTHEME
• PYRX_COLORTHEME, “1” = use dark mode
• PYRX_COLORTHEME, “” or nil = use dark mode

Applicable with dark mode on

• PYRX_COLORTHEME_OVERRIDE, “0” = don’t override (all black)
• PYRX_COLORTHEME_OVERRIDE, “1” = override colors (palette background color)
• PYRX_COLORTHEME_OVERRIDE, “” or nil = override colors (palette background color)