Removed serial port autodetection, fix bug in Prefs
Coordinator.java, Prefs.java, UsbSerialConnection.java:
-removed auto detecting serial port.  If a serial port is not specified on the command line or in the config file then the dummy serial driver is used. (fixes #27)
-fixed bug in Prefs.java.  preferences was static member, making some junit tests fail.
-commented out log messages in Prefs.readPreferences().  These messages were being printed out before the debug level was read.