push notification to many devices support

support for sending push notification to many devices via Gcm.
Fix gcm pushNotification and add test case for array of device tokens.
Fix gcm pushNotification and add test case for array of device tokens. Signed-off-by: Aris Kemper <aris.github@gmail.com>
Fix gcm pushNotification and add test case for array of device tokens. Signed-off-by: Aris Kemper <aris.github@gmail.com>
Merge pull request #41 from ariskemper/patch-2

GCM push notification support many device tokens