Resurrect Service Worker (#7108)

* Resolve #7106

* fix lint

* fix lint

* save lang in idb

* fix lint

* fix

* cache locale file

* fix lint

* ✌️

* wip

* fix [wip]

* fix [wip]

Co-authored-by: syuilo <Syuilotan@yahoo.co.jp>

package.json

@@ -130,7 +130,6 @@
 		"css-loader": "5.0.1",
 		"cssnano": "4.1.10",
 		"dateformat": "4.5.1",
-		"deep-entries": "3.1.0",
 		"diskusage": "1.1.3",
 		"double-ended-queue": "2.1.0-0",
 		"escape-regexp": "0.0.1",
@@ -155,6 +154,7 @@
 		"http-proxy-agent": "4.0.1",
 		"http-signature": "1.3.5",
 		"https-proxy-agent": "5.0.0",
+		"idb-keyval": "5.0.1",
 		"insert-text-at-cursor": "0.3.0",
 		"is-root": "2.1.0",
 		"is-svg": "4.2.1",