Bug 850693 - Create a NotificationHandler for each Fennec instance. r=kats

--HG--
rename : mobile/android/base/NotificationServiceClient.java => mobile/android/base/NotificationClient.java
rename : mobile/android/base/NotificationService.java => mobile/android/base/NotificationHandler.java
extra : rebase_source : 861bb500d9f1cd7cbc98a0c3628ddf7894e1e976