Restart ifmonitor from astrid daemon on "command:update_obsfreq" message

There was an OBSFREQ problem at the start of our session today because the ifmonitor script had crashed earlier in the day (unable to connect issues).  In addition to robustifying the ifmonitor script to recover from this more gracefully, I think it might be good to change the astrid daemon to handle the "command:update_obsfreq" message by restarting the ifmonitor process via circus.