calendar's popover: use GbScrolledWindow

This solve the problem of too many calendars making the window too tall.

Bug: https://bugzilla.gnome.org/show_bug.cgi?id=749459

data/ui/window.ui

@@ -333,21 +333,22 @@
     <signal name="event-activated" handler="search_event_selected" object="GcalWindow" swapped="no"/>
   </object>
   <object class="GtkPopover" id="calendar_popover">
-    <property name="visible">False</property>
-    <property name="can_focus">False</property>
     <property name="border_width">6</property>
+    <child>
+      <object class="GbScrolledWindow">
+        <property name="visible">True</property>
+        <property name="hscrollbar_policy">never</property>
+        <property name="min_content_height">80</property>
+        <property name="max_content_height">500</property>
         <child>
           <object class="GtkBox" id="calendar_box">
             <property name="visible">True</property>
-        <property name="can_focus">False</property>
             <property name="orientation">vertical</property>
             <property name="spacing">6</property>
             <child>
               <object class="GtkListBox" id="calendar_listbox">
                 <property name="visible">True</property>
-            <property name="can_focus">False</property>
                 <property name="hexpand">True</property>
-            <property name="vexpand">True</property>
                 <property name="selection_mode">none</property>
                 <signal name="row-activated" handler="source_row_activated" object="GcalWindow" swapped="no" />
                 <style>
@@ -355,7 +356,6 @@
                 </style>
               </object>
               <packing>
-            <property name="expand">False</property>
                 <property name="fill">True</property>
                 <property name="position">0</property>
               </packing>
@@ -370,14 +370,12 @@
                 <child>
                   <object class="GtkLabel" id="calendar_settings_label">
                     <property name="visible">True</property>
-                <property name="can_focus">False</property>
                     <property name="label" translatable="yes">Calendar Settings</property>
                     <property name="xalign">0</property>
                   </object>
                 </child>
               </object>
               <packing>
-            <property name="expand">False</property>
                 <property name="fill">True</property>
                 <property name="position">1</property>
               </packing>
@@ -385,6 +383,8 @@
           </object>
         </child>
       </object>
+    </child>
+  </object>
   <object class="GtkPopover" id="popover">
     <property name="visible">False</property>
     <property name="relative_to">views_stack</property>