Modified MobilabSignal to have a timestamp slot for when the timestamp
gets to Python.
Modified EnobioSignalHandler to not log raw data by default.  If you
define RAW_ENOBIO_LOG it will log data.  This is a compile time
flag.
Improved the MobilabSignal.getdata records the time
Modified NiDaqSignal to record the time stamp a sample is received; uses
the high resolution timer.
Made RawSignal require the last sample of a batch be 0; all devices
support adding space for the Python time stamp.  If it is not there there
is a programmatic problem.