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/plotting_widget/plotting.py

@@ -174,18 +174,17 @@ class Plotting:
         ax.plot(points_list[1], len(points_list[1]) * [0.5], linestyle="",
                 marker='s', markersize=2, zorder=constants.Z_ORDER['DOT'],
                 color=clr[colors[1]], picker=True, pickradius=3)
-        x = points_list[0] + points_list[1]
-        x = sorted(x)
+
         ax.set_ylim(-2, 2)
         self.plotting_axes.set_axes_info(
             ax, [len(points_list[0]), len(points_list[1])],
             sample_no_colors=[clr[colors[0]], clr[colors[1]]],
             sample_no_pos=[0.25, 0.75],
             chan_db_info=chan_db_info, linked_ax=linked_ax)
-        if linked_ax is None:
-            ax.x = x
-        else:
-            ax.linkedX = x
+
+        ax.x0 = points_list[0]
+        ax.x1 = points_list[1]
+
         ax.chan_db_info = chan_db_info
         return ax