Add "Night Mode" to PolyGlot

[DraqueT]

Cobolt looks nice. Maybe get some ideas from that color scheme? https://i.imgur.com/33fOZid.png

Revert hiding of menu option (not including feature in 2.3.3)

• [x] add entry to options
• [x] make option save to ini file
• [ ] make all extended objects respect setting
• [ ] make flashing (POptionPane) respect setting
• [ ] see whether other visual objects must be extended to respect
• [ ] either manually force form/dialog compliance or move compliance to superclasses