Update pl.po
Update pl.po

Add missing translations, replace fuzzy translations with proper ones and hopefully fix some mistakes.

Largely untested, as I currently don't have JWM installed anywhere, but hopefully it should work fine – there were no issues found when pasted to a PO editor.

I was thinking of changing plural forms to `"Plural-Forms: nplurals=4; plural=(n==1 ? 0 : (n%10>=2 && n%10<=4) && (n%100<12 || n%100>14) ? 1 : n!=1 && (n%10>=0 && n%10<=1) || (n%10>=5 && n%10<=9) || (n%100>=12 && n%100<=14) ? 2 : 3);\n"` but I decided not to overcomplicate it, especially as I don't know if plurals are used anywhere anyway. I just moved the line break a little higher after suggestion of Poedit.
joewing/jwm,joewing/jwm