Reorder translations and add missing prefixes

- files should be prefixed with code_ocean/
- the markdown editor is part of the application (helper)

config/locales/de/exercise_tip.yml

@@ -0,0 +1,9 @@
+---
+de:
+  activerecord:
+    attributes:
+      exercise_tip:
+        exercise: Aufgabe
+        parent_exercise_tip: Übergeordneter Tipp
+        rank: Rang
+        tip: Tipp