NMEA 2000 from file support

Add support for NMEA2000  input: add n2kProvider, that can read n2k sentences from a a file, run them through CANBoat analyzer to producen json and convert the json to SignalK nested format. In addition to the n2k support there is a new mechanism for configuring the providers in the settings file and a command line options -s to specify the settings file and --n2kfile=/foo/bar.n2kdata to specify the n2k file.