[AKQAKIEV-38] added  method load loadSpeakerSessions to ConfererService and it implementations, code refactioring
[AKQAKIEV-32] Implemented push notifications from server to the client
Added new entities on server Action and GcmRegistraion
Added logic of Database changes json creation
Added tests for server
Code refactoring
Merge branch 'develop' of https://github.com/biellou/Conferer into local develop

Conflicts:
	client/android/AKQAConferer/AndroidManifest.xml
	client/android/AKQAConferer/res/values/strings.xml
	client/android/AKQAConferer/src/com/akqa/kiev/android/conferer/StartActivity.java
	client/android/AKQAConferer/src/com/akqa/kiev/android/conferer/db/ConfererDatabase.java
	client/android/AKQAConferer/src/com/akqa/kiev/android/conferer/db/SessionDao.java
	client/android/AKQAConferer/src/com/akqa/kiev/android/conferer/service/ConfererService.java
	client/android/AKQAConferer/src/com/akqa/kiev/android/conferer/web/client/ConfererWebClient.java
	web/src/main/java/com/akqa/kiev/conferer/server/model/Conference.java