Change to use matplotlib's lim for zooming

closes #118 (closed)

When zooming before, downsample need to be recalculated and replot. With the reducing of data points, downsample isn't necessary anymore. SOHView now can use lim for zooming.

• Remove set_lim in PlottingWidget's subclasses.
• Recalculate total points for plot_time_dots, plot_multi_color_dots and plot_up_down_dots. (They were set when recreating axis before)
• Remove the condition to handle 'ax' or 'ax_wf' are already in c_data in SOHWidget and WaveformWidget. This case only takes place when a channel is replotted.

sohstationviewer/view/plotting/state_of_health_widget.py

@@ -66,16 +66,8 @@ class SOHWidget(MultiThreadedPlottingWidget):
         linked_ax = None
         if chan_db_info['linkedChan'] not in [None, 'None', '']:
             linked_ax = self.plotting_data1[chan_db_info['linkedChan']]['ax']
-        if 'ax' not in c_data:
-            ax = getattr(self.plotting, plot_functions[plot_type][1])(
-                c_data, chan_db_info, chan_id, None, linked_ax)
-            if ax is None:
-                return
-            c_data['ax'] = ax
-            ax.chan = chan_id
-            self.axes.append(ax)
-        else:
-            for artist in c_data['ax'].lines + c_data['ax'].collections:
-                artist.remove()
-            getattr(self.plotting, plot_functions[plot_type][1])(
-                c_data, chan_db_info, chan_id, c_data['ax'], linked_ax)
+        ax = getattr(self.plotting, plot_functions[plot_type][1])(
+            c_data, chan_db_info, chan_id, None, linked_ax)
+        c_data['ax'] = ax
+        ax.chan = chan_id
+        self.axes.append(ax)