add script to flash nrf51822

A script to flash softdevice hex file and application binary to nrf51822

+ To flash softdevice (arm-none-eabi-objcopy is needed)
```
python flash_nrf51822.py -s softdevice
```
+ To flash application binary
```
python flash_nrf51822.py -s softdevice
```

[More details](http://mbed.org/users/yihui/notebook/nrf51822-with-pyocd-and-arch/)