test: moved all db dependent tests to integration
test: added tests for notifications.clients
test: added tests for notifications.sender
notifications: minor refactoring in GcmApiKey
test: added tests for notifications.rest
notifications: added to and from json conversion to clients
notifications: removed manual Client adapters used by db
notifications: added tests for CachedClientDatastore
test: added tests for notifications.definitions
notifications: inject DbAccessor in JsonDbClientDatastore
notifications: removed views from JsonDbClientDatastore
test: added test for JsonDbClientDatastore