Added $timeout to avoid $digest already in progress errors

Hi Patrick,

I was getting "$digest already in progress" errors in my ionic project when I tried to use push:

> Error: [$rootScope:inprog] $digest already in progress
> http://errors.angularjs.org/1.2.17/$rootScope/inprog?p0=%24digest
>     at file:///android_asset/www/lib/ionic/js/ionic.bundle.js:7942:12
>     at beginPhase (file:///android_asset/www/lib/ionic/js/ionic.bundle.js:20690:15)
>     at Scope.$apply (file:///android_asset/www/lib/ionic/js/ionic.bundle.js:20479:11)
>     at null.<anonymous> (file:///android_asset/www/lib/push.js:15:18)
>     at Channel.subscribe (file:///android_asset/www/cordova.js:743:11)
>     at HTMLDocument.document.addEventListener (file:///android_asset/www/cordova.js:126:34)
>     at Object.$get (file:///android_asset/www/lib/push.js:14:14)
>     at Object.invoke (file:///android_asset/www/lib/ionic/js/ionic.bundle.js:11763:17)
>     at file:///android_asset/www/lib/ionic/js/ionic.bundle.js:11605:37
>     at getService (file:///android_asset/www/lib/ionic/js/ionic.bundle.js:11726:39) 

I fixed the problem adding $timeout to push.js as suggested in this stackoverflow answer:

http://stackoverflow.com/questions/12729122/prevent-error-digest-already-in-progress-when-calling-scope-apply/18996042#18996042

Best regards