separate root layout and plot-container layout

director.py

@@ -16,7 +16,8 @@ class Director:
         self.ti_add_pv = ti_add_pv = TextInput(value="", title="Add PV:")
         ti_add_pv.on_change("value", self.on_add_pv)
 
-        self.layout = layout = column(ti_add_pv)
+        self.plot_container = plot_container = column()
+        layout = column(ti_add_pv, plot_container)
         doc.add_root(layout)
 
 
@@ -60,8 +61,8 @@ class Director:
     def add_plot(self, a):
         print("Add plot:", a)
         fig = a.plt.fig
-#        self.layout.children.append(fig)
-        self.layout.children.insert(1, fig) # 1 to skip TextInput
+#        self.plot_container.children.append(fig)
+        self.plot_container.children.insert(0, fig)
         assert a.cb is None #TODO
         a.cb = self.doc.add_periodic_callback(a.update, 1000)
 
@@ -69,7 +70,7 @@ class Director:
     def remove_plot(self, a):
         print("Remove plot:", a)
         fig = a.plt.fig
-        self.layout.children.remove(fig)
+        self.plot_container.children.remove(fig)
         assert a.cb is not None #TODO
         self.doc.remove_periodic_callback(a.cb)