Updates unhandledrejection handler to not relay on JitsiMeetJS being global and fixes onerror handler.

JitsiMeetJS.js

 
                 if (oldOnErrorHandler)
                     oldOnErrorHandler(message, source, lineno, colno, error);
-            }
+            }.bind(this);
 
             // if an old handler exists also fire its events
             var oldOnUnhandledRejection = window.onunhandledrejection;
             window.onunhandledrejection = function(event) {
 
-                JitsiMeetJS.getGlobalOnErrorHandler(
+                this.getGlobalOnErrorHandler(
                     null, null, null, null, event.reason);
 
                 if(oldOnUnhandledRejection)
                     oldOnUnhandledRejection(event);
-            };
+            }.bind(this);
         }
 
         return RTC.init(options || {});