pkg/openthread: add OpenThread core

Makefile.dep

drivers/at86rf2xx/at86rf2xx_netdev.c

drivers/include/net/netdev.h

makefiles/pseudomodules.inc.mk

pkg/openthread/Makefile

pkg/openthread/Makefile.include

pkg/openthread/contrib/Makefile

pkg/openthread/contrib/netdev/Makefile

pkg/openthread/contrib/netdev/openthread_netdev.c

pkg/openthread/contrib/openthread.c

pkg/openthread/contrib/platform_alarm.c

pkg/openthread/contrib/platform_diag.c

pkg/openthread/contrib/platform_functions_wrapper.c

pkg/openthread/contrib/platform_logging.c

pkg/openthread/contrib/platform_misc.c

pkg/openthread/contrib/platform_radio.c

pkg/openthread/contrib/platform_random.c

pkg/openthread/contrib/platform_settings.c

pkg/openthread/contrib/platform_uart.c

pkg/openthread/include/ot.h