start a radio tx thread to centralize transmit requests
update defconfig

fix all apps to init the system before using devices.
We still have a problem: when sysdaemon is used as startup, and we run additional apps, the radio device FDs are not valid anymore. we need to fix this by sending radio packets to the sysdaemon with a thread and work queue.

add beacon app, some Kconfig improvements. Repeated transmission reveals a transmission problem where the FIFO is filled but transmission does not start.