[RN] Fix iOS lockups / resprings

Apparently iOS doesn't like dangling background tasks very much, so update the
background timers plugin with a version which fixes this.

https://github.com/ocetnik/react-native-background-timer/pull/38

Also accomodate for the API changes upstream.

Credits to @lyubomir for finding the needle in the haystack.

package.json

     "react-dom": "15.4.2",
     "react-i18next": "4.1.0",
     "react-native": "0.42.3",
-    "react-native-background-timer": "1.0.2",
+    "react-native-background-timer": "saghul/react-native-background-timer#ios-end-task",
     "react-native-immersive": "0.0.5",
     "react-native-keep-awake": "2.0.4",
     "react-native-locale-detector": "1.0.1",

react/features/base/lib-jitsi-meet/native/polyfills-browser.js

     // Required by:
     // - lib-jitsi-meet
     // - Strophe
-    global.clearTimeout = window.clearTimeout = BackgroundTimer.clearTimeout;
-    global.clearInterval = window.clearInterval = BackgroundTimer.clearInterval;
-    global.setInterval = window.setInterval = BackgroundTimer.setInterval;
-    global.setTimeout = window.setTimeout = BackgroundTimer.setTimeout;
+    global.clearTimeout = window.clearTimeout
+        = BackgroundTimer.clearTimeout.bind(BackgroundTimer);
+    global.clearInterval = window.clearInterval
+        = BackgroundTimer.clearInterval.bind(BackgroundTimer);
+    global.setInterval = window.setInterval
+        = BackgroundTimer.setInterval.bind(BackgroundTimer);
+    global.setTimeout = window.setTimeout
+        = BackgroundTimer.setTimeout.bind(BackgroundTimer);
 
 })(global || window || this); // eslint-disable-line no-invalid-this