BLE API refactoring and synchronization logic

BLE code was split in two parts:

- ble-api: the core (common part)
  Can be found at http://mbed.org/users/mbed_official/code/ble-api
- nRF51822: the Nordic specific implementation for the ble-api library
  Can be found at http://mbed.org/teams/Nordic-Semiconductor/code/nRF51822

The code was slightly modified to follow this refactoring. The tests were also updated
to follow this new structure.
The code should now automatically sync from github to the above repositories.

libraries/ble/nRF51822/btle/btle.cpp

@@ -33,8 +33,8 @@
 #include "pstorage.h"
 
 #include "hw/GapEvents.h"
-#include "hw/nRF51822n/nRF51Gap.h"
-#include "hw/nRF51822n/nRF51GattServer.h"
+#include "nRF51Gap.h"
+#include "nRF51GattServer.h"
 
 static void service_error_callback(uint32_t nrf_error);
 void        assert_nrf_callback(uint16_t line_num, const uint8_t * p_file_name);

libraries/ble/nRF51822/nRF51822n.h

@@ -25,8 +25,8 @@
 #include "mbed.h"
 #include "blecommon.h"
 #include "hw/BLEDevice.h"
-#include "hw/nRF51822n/nRF51Gap.h"
-#include "hw/nRF51822n/nRF51GattServer.h"
+#include "nRF51Gap.h"
+#include "nRF51GattServer.h"
 
 /**************************************************************************/
 /*!