Update app.json

Updated and made changes to the translations:
- corrected some spelling and grammar mistakes
- changed some literal translations to make them sound more natural
- changed all instances of HP to PZ (Pol. punkty zdrowia), which makes sense, since the PL version will only be used by people who don't know English - HP would not mean anything to them
- updated capitalization - Polish DOES NOT capitalize words that are not at the beginning of the sentence or that are not proper names

The previous translator did an excellent job though and I'm ready to discuss some of my changes.