SSO/OpenID: Use a mobile-redirect route (Fixes #2379 and #2381)

- Implement /auth/openid/mobile-redirect this will redirect to an app-link like audiobookshelf://oauth
- An app must provide an `redirect_uri` parameter with the app-link in the authorization request to /auth/openid
- The user will have to whitelist possible URLs, or explicitly allow all
- Also modified MultiSelect to allow to hide the menu/popup

client/strings/de.json

@@ -337,6 +337,8 @@
   "LabelMinute": "Minute",
   "LabelMissing": "Fehlend",
   "LabelMissingParts": "Fehlende Teile",
+  "LabelMobileRedirectURIs": "Erlaubte Weiterleitungs-URIs für die mobile App",
+  "LabelMobileRedirectURIsDescription": "Dies ist eine Whitelist gültiger Umleitungs-URIs für mobile Apps. Der Standardwert ist <code>audiobookshelf://oauth</code>, den Sie entfernen oder durch zusätzliche URIs für die Integration von Drittanbieter-Apps ergänzen können. Die Verwendung eines Sternchens (<code>*</code>) als alleiniger Eintrag erlaubt jede URI.",
   "LabelMore": "Mehr",
   "LabelMoreInfo": "Mehr Info",
   "LabelName": "Name",

client/strings/en-us.json

@@ -343,6 +343,8 @@
   "LabelMinute": "Minute",
   "LabelMissing": "Missing",
   "LabelMissingParts": "Missing Parts",
+  "LabelMobileRedirectURIs": "Allowed Mobile Redirect URIs",
+  "LabelMobileRedirectURIsDescription": "This is a whitelist of valid redirect URIs for mobile apps. The default one is <code>audiobookshelf://oauth</code>, which you can remove or supplement with additional URIs for third-party app integration. Using an asterisk (<code>*</code>) as the sole entry permits any URI.",
   "LabelMore": "More",
   "LabelMoreInfo": "More Info",
   "LabelName": "Name",