Formatting issues resolved

There were some formatting issues with the PDF versions, some images were cut either horizontally or vertically, so we have fixed this  (sorry about that). No issues with any of the ePUB versions.

We've made corrections to the Polish text, as submitted by Tomasz Stecko.
- Lesson 3 Cat: 'kartke' was changed to 'kartkę'.
- Preface text: 'znąjdują' changed to 'znajdują'.
-(Lesson 3 Fox: text changed to 'Lis wywraca biurko na lewą stronę.'
-Lesson 5 Owl: text changed to 'Sowa rozumie, jak działa pokój.'