Add dark theme about real-file.extnsn

[ygz213]

Added in R-F.E v3.1.

[ygz213]

I'll try to add this feature in the next version and if I fail I will add help wanted label

[ygz213]

I have learned create a checked checkbutton but I won't come back to old design.

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I could not add it. I think there is 2 options to add dark theme:

• Add special dark widgets for each label, entry, button etc. (Code will be terrible) (Example is below)

if dark_theme == False:
    Normal Label, entry etc.
if dark_theme == True:
    Dark Label, entry etc.

• Add dark themed version (Will cause unnecessary files)

app/
    main.py
    main_turkish.py
    main_darkthemed.py
    main_turkish_darkthemed.py

So I won't add dark theme for now. (Everyone can create pull request)