Cache images via service worker

Improves the image request logic by making it possible to check if an image is cached.
In case an image is cached, it does not need to be put into the image queue because it won't be sent to the server.

public/locales/en.json

@@ -1269,9 +1269,9 @@
     "clear_cache": {
       "label": {
         "description": "The cache of the client (browser, electron) should get cleared alongside it, otherwise, the client cache will keep getting used",
-        "failure": "Could not clear the server cache",
-        "success": "Cleared the server cache",
-        "title": "Clear server cache"
+        "failure": "Could not clear the cache",
+        "success": "Cleared the cache",
+        "title": "Clear cache"
       }
     },
     "default_value": "{{value}}<0>($t(global.label.default))</0>",