remove serialport polling, etc.

change from polling node-serialport to fs.watch()ing /dev/ to find out
when new serial devices have been plugged in.  also, add disconnect
logic as referenced in voodootikigod/node-serialport #349 (though it
doesn't seem that this fixes anything) and improve the process for
keeping the chillhub-devices in sync with /dev/ttyACM*.  finally, fix
some minor flaws in the code.
Merge branch 'master' of https://github.com/FirstBuild/Chillhub