Update translations for new difficulty values

src/main/webapp/i18n/de/exercise.json

@@ -51,10 +51,11 @@
         "plural": "Voraussetzungen"
       },
       "difficulty": "Schwierigkeit",
-      "simple": "Simple",
+      "simple": "Einfach",
+      "easy": "Einfach",
       "medium": "Mittel",
-      "advanced": "Fortgeschritten",
-      "none": "Keine",
+      "difficult": "Schwierig",
+      "advanced": "Schwierig",
       "educationalLevel": {
         "singular": "Bildungsniveau",
         "plural": "Bildungsniveau"

src/main/webapp/i18n/en/exercise.json

@@ -51,10 +51,11 @@
         "plural": "Requirements"
       },
       "difficulty": "Difficulty",
-      "simple": "Simple",
+      "simple": "Easy",
+      "easy": "Easy",
       "medium": "Medium",
-      "advanced": "Advanced",
-      "none": "None",
+      "difficult": "Difficult",
+      "advanced": "Difficult",
       "educationalLevel": {
         "singular": "Educational Level",
         "plural": "Educational Level"