Changing defaults MUC affiliation (#385):

* For Peertube moderators/admins, we add a button "Promote". Clicking on it will promote them as MUC owner.

client/videowatch/button.ts

@@ -10,7 +10,7 @@ interface displayButtonOptionsBase {
 }
 
 interface displayButtonOptionsCallback extends displayButtonOptionsBase {
-  callback: () => void | boolean
+  callback: () => void | boolean | Promise<void>
 }
 
 interface displayButtonOptionsHref extends displayButtonOptionsBase {