RequestQueue has been changed

If we click back from the activity the API object still the same because it's a static object
and if we navigate again to the activity, we are creating a new RequestQueue, but in Api.get(requestQueue) the API object is not null so here we are dealing with two request queues and the callback functions is never called.
Move glide configuration and requestqueue from the activity to the Api
class
Merge pull request #87 from hegazy/master

Api dealing with outdated RequestQueue