Polish Language

Only the core files (strings.js) but "Getting Started" is comming very
soon.
Updated to sprint 22

Added all strings missing from sprint 21
Getting Started added

- Gettting Started translated to polish
- Getting Started connected in the urls.js
Fixes.

- all fixes like typos, untranslated strings etc spotted by  jbalsas
- image of polish version added
Small fixes made for bugs found white using pl translation on Sprint 22
Peer review.
Merge pull request #2 from RadekJurzysta/patch-2

Peer review of Polish translation