Edit TimeSeries internals: use Coordinates
Edit TimeSeries internals: use Coordinates

* self.timeseries is now a Coordinates instance (not a 2d ndarray): this way is
  easier to clear NaNs (.clear_x, and .clear_y attributes)
* 'label' parameter disappears
* ts parameter input is either a Coordinates instance, or a 2d ndarray

LeBarbouze/tunacell