Add theme URL param and adjust cpd theme based on it.

Signed-off-by: Timo K <toger5@hotmail.de>

src/UrlParams.ts

@@ -130,6 +130,11 @@ export interface UrlParams {
    * This is useful for video rooms.
    */
   returnToLobby: boolean;
+  /**
+   * The theme to use for element call.
+   * can be "light", "dark", "light-hc" or "dark-hc".
+   */
+  theme: string | null;
 }
 
 // This is here as a stopgap, but what would be far nicer is a function that
@@ -229,6 +234,7 @@ export const getUrlParams = (
     perParticipantE2EE: parser.getFlagParam("perParticipantE2EE"),
     skipLobby: parser.getFlagParam("skipLobby"),
     returnToLobby: parser.getFlagParam("returnToLobby"),
+    theme: parser.getParam("theme"),
   };
 };