Update challenge.json

review:
vocabulary changes, fixed typos.
Update character.json

typos; du -> Du (I need to set autocorrect on this...)
Update contrib.json

typos, corrections.
Update front.json

typos, du->Du
Update generic.json

typos
Update groups.json

"Can't like your own message" ... ...
typos and du-Du
Update limited.json

even hier du-Du
Update npc.json

fixed some mistakes. du-Du
Update pets.json

several fixes, "drops" ...
Update quests.json

minor fixes
Update rebirth.json

history -> verlauf du-Du
Update settings.json

"verlauf" "Du"
Update subscriber.json

fixes
Update tasks.json

fixes "Du"
Merge pull request #135 from luveluen/develop

Spelling and Vocabulary