Update translations from Transifex

Update translations from Transifex

- Add Polish and Korean translations
- Update quassel.pot (5 new messages)

Many thanks to:
 - cs: Tomáš Chvátal <tomas.chvatal@gmail.com>
 - da: Per Nielsen
 - el: differentreality <differentreality@gmail.com>, Theofilos Intzoglou <int.teo@gmail.com>
 - fr: Dorian <munto@free.fr>
 - gl: Condex <elgomaisa@gmail.com>
 - ko: Tae-Hoon KWON <zerolaunch@naver.com>
 - nl: simonphilips <simon.philips@gmail.com>
 - pl: derpella <matwa@poczta.pl>
 - ru: sfionov <fionov@gmail.com>
 - uk: Yuri Chornoivan <yurchor@ukr.net>