Add Vocab Trainer feature with routing, database schema, and translations

- Introduced Vocab Trainer functionality, including new routes for managing languages and chapters.
- Implemented database schema for vocab-related tables to ensure data integrity.
- Updated navigation and UI components to include Vocab Trainer in the social network menu.
- Added translations for Vocab Trainer in both German and English locales, enhancing user accessibility.

frontend/src/i18n/locales/en/navigation.json

@@ -20,6 +20,7 @@
             "usersearch": "User search",
             "forum": "Forum",
             "gallery": "Gallery",
+            "vocabtrainer": "Vocabulary trainer",
             "blockedUsers": "Blocked users",
             "oneTimeInvitation": "One-time invitations",
             "diary": "Diary",
@@ -27,6 +28,9 @@
             "m-erotic": {
                 "pictures": "Pictures",
                 "videos": "Videos"
+            },
+            "m-vocabtrainer": {
+                "newLanguage": "New language"
             }
         },
         "m-minigames": {