tdf#113859 Make it possible to select every widget with tab

On the shadowtab page of a figure (eg. rectangle, ellipse) the widgets
that modify the shadow can now be selected using the tab button.
Removed an "invisible" alignment from the ui file that caused the problem.

Change-Id: Id833302d42b9c1f2df640135473f159c0a3af4f7
Reviewed-on: https://gerrit.libreoffice.org/45444Reviewed-by: Tamás Zolnai <tamas.zolnai@collabora.com>
Tested-by: Tamás Zolnai <tamas.zolnai@collabora.com>

cui/uiconfig/ui/shadowtabpage.ui

@@ -131,21 +131,6 @@
                     </child>
                     <child>
                       <object class="GtkAlignment" id="alignment3">
-                        <property name="visible">True</property>
-                        <property name="can_focus">False</property>
-                        <property name="halign">start</property>
-                        <property name="left_padding">12</property>
-                        <child>
-                          <placeholder/>
-                        </child>
-                      </object>
-                      <packing>
-                        <property name="left_attach">0</property>
-                        <property name="top_attach">0</property>
-                      </packing>
-                    </child>
-                    <child>
-                      <object class="GtkAlignment" id="alignment4">
                         <property name="visible">True</property>
                         <property name="can_focus">False</property>
                         <property name="left_padding">12</property>
@@ -165,7 +150,7 @@
                       </packing>
                     </child>
                     <child>
-                      <object class="GtkAlignment" id="alignment5">
+                      <object class="GtkAlignment" id="alignment4">
                         <property name="visible">True</property>
                         <property name="can_focus">False</property>
                         <property name="left_padding">12</property>