Feature for users to hide/show and reorder channels

Closes #188 (closed)

sohstationviewer/model/general_data/data_structures.MD

@@ -25,8 +25,9 @@ Note: log_data for RT130's dataset has only one channel: SOH
         'data' (np.array): data that has been trimmed and down-sampled for plotting
         'chan_db_info' (dict): the plotting parameters got from database
             for this channel - dict,
-        ax: axes to draw the channel in PlottingWidget
-        ax_wf (matplotlib.axes.Axes): axes to draw the channel in WaveformWidget
+        'ax': axes to draw the channel in PlottingWidget
+        'ax_wf' (matplotlib.axes.Axes): axes to draw the channel in WaveformWidget
+        'visible': flag to show or hide channel
     }
 }