Create pl.json

Polish translation
99,5% completed (now is 2013-06-18 18:43 UTC+0)
OFC, polish special chars are changed to Unicode codes, as in other languages.
BTW. I hope that if translation will not have needed lines, there will be used lines from English version, am I right?
Merge pull request #104 from ciddaemon/patch-2

Create pl.json