[IMP] improves the scrolling behaviour

the mail menu is a client action, so not subject to the same template
as regular views.  so, it had to be patched to properly scroll like
other views (meaning: the 'header', left menu and top menu are fixed)

Also, changes the width of the searchbbar into a min-width css property,
to allow it to grow more.  The reason is that we don't want the searchbox
to take two lines (or more), which will force the view_manager_header to be
higher, and which will cause slight issues with the scrollbar (absolutely
positioned)

addons/mail/static/src/css/mail.css

@@ -683,6 +683,20 @@
     margin-right: 212px;
 }
 
+/* ----------- SCROLLING AREA ----------- */
+.openerp .oe_mail_wall .oe_view_manager_header {
+    height: 47px;
+}
+
+.openerp .oe_mail_wall > div {
+    position: absolute;
+    overflow: auto;
+    top: 48px;
+    bottom: 0;
+    left: 0;
+    right: 0;
+}
+
 /* ----------- INBOX INTEGRATION ----------- */
 
 .openerp .oe_mail_wall .oe_mail{

addons/mail/static/src/xml/mail.xml

@@ -191,9 +191,11 @@
             </tr>
           </tbody>
         </table>
-        <div class="oe_searchview_drawer_container"/>
-        <div class="oe_mail-placeholder"></div>
-        <aside class="oe_mail_wall_aside"></aside>
+        <div>
+            <div class="oe_searchview_drawer_container"/>
+            <div class="oe_mail-placeholder"></div>
+            <aside class="oe_mail_wall_aside"></aside>
+        </div>
     </div>
 
     <!--