[gnome-control-center] notifications: Use a HdyColumn

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 42d64e3baf0db4a7faecc20802e486b7beb0e908
Author: Adrien Plazas <kekun plazas laposte net>
Date:   Wed Oct 24 15:03:11 2018 +0200

    notifications: Use a HdyColumn
    
    This better adapts the panel's size to the window's size, allowing it to
    look good on both large and narrow windows.

 panels/notifications/cc-notifications-panel.ui | 33 ++++++--------------------
 1 file changed, 7 insertions(+), 26 deletions(-)
---
diff --git a/panels/notifications/cc-notifications-panel.ui b/panels/notifications/cc-notifications-panel.ui
index 7527001d8..8b13d3f6b 100644
--- a/panels/notifications/cc-notifications-panel.ui
+++ b/panels/notifications/cc-notifications-panel.ui
@@ -5,7 +5,6 @@
     <property name="visible">True</property>
     <child>
       <object class="GtkScrolledWindow" id="main_scrolled_window">
-        <property name="height_request">400</property>
         <property name="visible">True</property>
         <property name="can_focus">True</property>
         <property name="hscrollbar_policy">never</property>
@@ -15,36 +14,18 @@
             <property name="visible">True</property>
             <property name="can_focus">False</property>
             <child>
-              <object class="GtkBox">
+              <object class="HdyColumn">
                 <property name="visible">True</property>
-                <property name="can_focus">False</property>
-
-                <!-- Stub boxes to make the content cover 1/3 of the screen -->
-                <child>
-                  <object class="GtkBox">
-                    <property name="visible">True</property>
-                    <property name="can_focus">False</property>
-                    <property name="hexpand">True</property>
-                  </object>
-                </child>
-
-                <child>
-                  <object class="GtkBox">
-                    <property name="visible">True</property>
-                    <property name="can_focus">False</property>
-                    <property name="hexpand">True</property>
-                  </object>
-                  <packing>
-                    <property name="pack_type">end</property>
-                  </packing>
-                </child>
-
-                <!-- Content -->
+                <property name="maximum_width">600</property>
+                <property name="linear_growth_width">400</property>
+                <property name="margin_top">32</property>
+                <property name="margin_bottom">32</property>
+                <property name="margin_start">12</property>
+                <property name="margin_end">12</property>
                 <child>
                   <object class="GtkBox" id="main_box">
                     <property name="visible">True</property>
                     <property name="can_focus">False</property>
-                    <property name="margin">32</property>
                     <property name="orientation">vertical</property>
                     <property name="hexpand">True</property>
                     <child>