Plot: added __slots__
TimeSeriesPlot: changes to set_time_format

    - set 'gps' as default arg to format
    - added auto-scaling
AutoTimeFormatter: implemented auto-scaling

    - added time auto-scaling, with hacks for hours to make plots look
      nice
TimeSeries.fetch: updated ndschanneltype default

    - fetch defaults to RAW | STREND | MTREND