book: Adapt spacing and margin of todo app

Author: Hofer-Julian

book/listings/todo/6/resources/window.ui

@@ -52,11 +52,11 @@
             <property name="child">
               <object class="GtkBox">
                 <property name="orientation">vertical</property>
-                <property name="spacing">18</property>
-                <property name="margin-top">24</property>
-                <property name="margin-bottom">24</property>
+                <property name="margin-top">12</property>
+                <property name="margin-bottom">12</property>
                 <property name="margin-start">12</property>
                 <property name="margin-end">12</property>
+                <property name="spacing">12</property>
                 <child>
                   <object class="GtkEntry" id="entry">
                     <property name="placeholder-text" translatable="yes">Enter a Task…</property>

book/listings/todo/7/resources/window.ui

@@ -164,11 +164,11 @@
                             <property name="child">
                               <object class="GtkBox">
                                 <property name="orientation">vertical</property>
-                                <property name="spacing">18</property>
-                                <property name="margin-top">24</property>
-                                <property name="margin-bottom">24</property>
+                                <property name="margin-top">12</property>
+                                <property name="margin-bottom">12</property>
                                 <property name="margin-start">12</property>
                                 <property name="margin-end">12</property>
+                                <property name="spacing">12</property>
                                 <child>
                                   <object class="GtkEntry" id="entry">
                                     <property name="placeholder-text" translatable="yes">Enter a Task…</property>