Simplify and beautify the Similarity Search dialog

* Remove unnecessary containers and unhelpful frame
* Center main container
* Right-align labels to remove large gaps between controls
* A bit of separation for the Help button

This should serve as a model for similar dialogs.

Change-Id: I1964e8909159506484950df9d8ef7283809cce5f
Reviewed-on: https://gerrit.libreoffice.org/13057Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

cui/uiconfig/ui/similaritysearchdialog.ui

@@ -59,6 +59,7 @@
                 <property name="visible">True</property>
                 <property name="can_focus">True</property>
                 <property name="receives_default">True</property>
+                <property name="margin_right">6</property>
                 <property name="use_stock">True</property>
                 <property name="image_position">top</property>
               </object>
@@ -77,35 +78,20 @@
             <property name="position">0</property>
           </packing>
         </child>
-        <child>
-          <object class="GtkFrame" id="Selection">
-            <property name="visible">True</property>
-            <property name="can_focus">False</property>
-            <property name="label_xalign">0</property>
-            <property name="shadow_type">none</property>
-            <child>
-              <object class="GtkAlignment" id="alignment3">
-                <property name="visible">True</property>
-                <property name="can_focus">False</property>
-                <property name="top_padding">6</property>
-                <property name="left_padding">12</property>
-                <child>
-                  <object class="GtkBox" id="box1">
-                    <property name="visible">True</property>
-                    <property name="can_focus">False</property>
-                    <property name="orientation">vertical</property>
-                    <property name="spacing">6</property>
         <child>
           <object class="GtkGrid" id="grid1">
             <property name="visible">True</property>
             <property name="can_focus">False</property>
+            <property name="halign">center</property>
+            <property name="hexpand">True</property>
+            <property name="vexpand">True</property>
             <property name="row_spacing">6</property>
             <property name="column_spacing">12</property>
             <child>
               <object class="GtkLabel" id="label2">
                 <property name="visible">True</property>
                 <property name="can_focus">False</property>
-                            <property name="xalign">0</property>
+                <property name="xalign">1</property>
                 <property name="label" translatable="yes">_Exchange characters:</property>
                 <property name="use_underline">True</property>
                 <property name="mnemonic_widget">otherfld</property>
@@ -119,7 +105,7 @@
               <object class="GtkLabel" id="label3">
                 <property name="visible">True</property>
                 <property name="can_focus">False</property>
-                            <property name="xalign">0</property>
+                <property name="xalign">1</property>
                 <property name="label" translatable="yes">_Add characters:</property>
                 <property name="use_underline">True</property>
                 <property name="mnemonic_widget">longerfld</property>
@@ -133,7 +119,7 @@
               <object class="GtkLabel" id="label4">
                 <property name="visible">True</property>
                 <property name="can_focus">False</property>
-                            <property name="xalign">0</property>
+                <property name="xalign">1</property>
                 <property name="label" translatable="yes">_Remove characters:</property>
                 <property name="use_underline">True</property>
                 <property name="mnemonic_widget">shorterfld</property>
@@ -196,27 +182,6 @@
               </packing>
             </child>
           </object>
-                      <packing>
-                        <property name="expand">False</property>
-                        <property name="fill">True</property>
-                        <property name="position">0</property>
-                      </packing>
-                    </child>
-                  </object>
-                </child>
-              </object>
-            </child>
-            <child type="label">
-              <object class="GtkLabel" id="label1">
-                <property name="visible">True</property>
-                <property name="can_focus">False</property>
-                <property name="label" translatable="yes">Settings</property>
-                <attributes>
-                  <attribute name="weight" value="bold"/>
-                </attributes>
-              </object>
-            </child>
-          </object>
           <packing>
             <property name="expand">False</property>
             <property name="fill">True</property>