de: update string.js

corrected existing translations
- typos
- added missing spaces which were very annoying since the words were then together
- minor changes according design guide lines https://github.com/doublespeakgames/adarkroom/wiki/Design-Guide#narrative
     - since nouns are capitalized in German, previous translators must have accidentally left some words capitalized, which was inconsistent with the rest
     - light fire -> "feuer entfachen" instead of "feuer machen", which is consistent with the same use of the word "light" in other situations
     - sammel holz -> holz sammeln, since the player should not be adressed directly with an imperative, and none of the other buttons (like feuer schüren) had the imperative (which would then be schüre feuer)