UI - Make light/dark themes customisable via Preferences

[tadayosi]

Preferences -> Home -> UI section can provide the theme toggle with system/light/dark options.

[tadayosi]

@grgrzybek @phantomjinx @jsolovjo Maybe this feature is something we've all been looking for.

[VishakhaVB]

Hi @tadayosi, I’d like to work on this feature. I’ll review the current preferences and theme handling implementation, then work on adding configurable system/light/dark theme options in the UI preferences section.

[grgrzybek]

PR:

• Theme selector #2131