Update locale.de.yml

German localization full reworked, maybe reviewed
Most important change: added ui.item-price. Without the price for customers isn't shown in the lore. (no en-fallback)
~~Added VIM modeline, because file isn't saved as .yml within plugin-directory~~ (better rename file to .yml: https://github.com/possi/dtlTraders/commit/653ffecfc0012546721e2bc43efa1a15109ff9d3#diff-c5b56153f9d64bd487cd40c6dd9ac3b7R80)