pkg/openwsn: update to current openwsn version

Updates the used OpenWSN version to current upstream and introduces a BSP implemented using RIOT peripheral interfaces.
Currently supported platforms are iot-lab_M3 and fox due to some remaining dependencies not tackled by at86rf231's netdev implementation and needed additions to the netdev interface in general.
You could use `uart0_readc` and `uart0_putc` instead.