Implement LBLEPeripheral::notifyAll for requst #11

[pablosun]

• Add a new method notifyAll() that broadcast to all living connections to LBLEPeripheral
• The connection handle is passed down from LBLEPeripheral to the characteristic object
• Move the definition of LBLEValueBuffer from LBLECentral.h to LBLE.h
• The object serializes its current value to LBLEValueBuffer and then calls parent class helper method _notify
• The value buffer is then passed down to the LinkIt SDK API bt_gatts_send_charc_value_notification_indication

Since notification is a fire-and-forget action, we don't wait for client side ACK events.