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.
Merge branch 'nordic_structure'