nRF51822 (BLE)

This is a RIOT port to the Nordic nRF51822 boards pca10000 and pca10005.
Containing UART, GPIO, Timer, Radio/BLE (still receiving issues).

This PR depends on:
 - #1291
I'm not touching the copyrights in the code. Just added the authors. Should the copyright always refer to Freie Universität Berlin?