Show time label on top of ruler

Closes #71 (closed)

sohstationviewer/view/plotting/plotting_widget/plotting_widget.py

@@ -461,6 +461,11 @@ class PlottingWidget(QtWidgets.QScrollArea):
             for w in self.peer_plotting_widgets:
                 w.set_rulers_invisible()
                 w.zoom_marker1_shown = False
+                try:
+                    self.ruler_text.remove()
+                    self.ruler_text = None
+                except AttributeError:
+                    pass
                 w.draw()
         return super(PlottingWidget, self).keyPressEvent(event)