Fixing long usernames (#2821)

* Submitting a fix for popover titles

* Fixing heading for channels

* Fixing other minor corner cases for long username

webapp/sass/responsive/_mobile.scss

@@ -11,6 +11,10 @@
         }
     }
 
+    .user-popover {
+        pointer-events: none;
+    }
+
     .signup-team__container {
         font-size: 1em;
     }