Major updates on polish language

Major updates on polish language
1. Changed Book translation from księga => podręcznik (księga is very old word, and thus not fit to the app. Podręcznik is word for book used in school and fits much more to the documentation site)
2. Changed Entity transaltion from encja => obiekt (encja is word used in IT world, common people doesn't know what it is. Obiekt (object) fits better for no IT geeks and explains them more than word encja)
3. Added Shelf/Bookshelf transaltion. Now they are named Półka/Półki
4. Changed Draft translation from szkic => wersja robocza (in every system like wordpress/wiki etc. the word for draft is wersja robocza. Szkic is word for draft of an image)
5. Fixed typos
6. Fixed unfit plural words when they were not needed