first shot at JSON RPC

opens another port at QEMUPORT+2
runs in a separate thread
share backend among threads

to be able to access the backend from within the rpc thread it
needs to be shared. Since socket objects apparently are not shared
the managment loop has to be in a separate thread with a queue.
make list of valid commands
fix audio file name
move alarm handler to be available ASAP
move save_results to bmwqemu