Sends key-events to remote devices. The payload structure corresponds basically
to that of remote key-presses in the mousepad-plugin (with the exception of the
"sendAck"-flag) , e.g.:

{
    "key": "a",
    "specialKey": 12,
    "shift": false,
    "ctrl": false,
    "alt": false,
    "sendAck": true
}

If "specialKey" is a valid keycode according to the internal map (1 <= x <= 32),
the event is interpreted as a special event and the contents of "key" are not
considered.

"key" may contain multi-char strings for performance reasons. In that case,
the peer is expected to print the whole string.

If "sendAck" is set to true, the device expects the remote peer to echo the
event in case it could be handled. This can be used to determine whether the
remote device is ready to accept remote keypresses.