feat: refactor email tagging system to use labels instead of colors

- Updated EmailContextMenu to replace color tag functionality with label tags.
- Modified EmailListItem to display label badges for emails based on keywords.
- Enhanced EmailViewer to include a tag picker for emails.
- Adjusted ThreadListItem to show label badges for email subjects.
- Added tests for email list item and keyword settings to ensure proper functionality of the new tagging system.
- Updated localization files to reflect changes from color tags to labels in multiple languages.

locales/de/common.json

@@ -155,9 +155,10 @@
     "back_to_list": "Zurück zur Liste",
     "message_details": "Nachrichtendetails",
     "more_reply_options": "Weitere Antwortoptionen",
-    "set_color": "Farbe festlegen",
+    "set_color": "Label setzen",
+    "tag": "Label",
     "more_actions": "Weitere Aktionen",
-    "remove_color": "Farbe entfernen",
+    "remove_color": "Label entfernen",
     "more_count": "+{count} weitere",
     "characters_count": "{count} Zeichen",
     "quick_reply_placeholder": "Eine kurze Antwort schreiben...",
@@ -929,8 +930,8 @@
     "delete": "Löschen",
     "mark_as_spam": "Spam melden",
     "not_spam": "Kein Spam",
-    "color_tag": "Farb-Tag",
-    "remove_color": "Farbe entfernen",
+    "color_tag": "Label",
+    "remove_color": "Label entfernen",
     "items_selected": "{count} E-Mails ausgewählt"
   },
   "shortcuts": {