Calibre web widget (#1855)

* Add widget for calibre-web with reverse-proxy auth

* Add custom proxy

* Get it working

* Fix lint issues

* Calibreweb widget: Handle empty series / authors / books

* Switch to new opds stats endpoint

* Remove calibre-web custom proxy handler

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Co-authored-by: shamoon <4887959+shamoon@users.noreply.github.com>

public/locales/en/common.json

@@ -667,6 +667,12 @@
         "monitoring": "Monitoring",
         "updates": "Updates"
     },
+    "calibreweb": {
+        "books": "Books",
+        "authors": "Authors",
+        "categories": "Categories",
+        "series": "Series"
+    },
     "jdownloader": {
         "downloadCount": "Queue",
         "downloadBytesRemaining": "Remaining",