[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>
 
     <!--

addons/web/static/src/css/base.css

@@ -1150,7 +1150,7 @@
 .openerp .oe_application > div > .oe_view_manager > .oe_view_manager_body {
   position: absolute;
   overflow: auto;
-  top: 90px;
+  top: 91px;
   bottom: 0;
   left: 0;
   right: 0;
@@ -1391,7 +1391,7 @@
   float: right;
   padding: 1px 0;
   line-height: 18px;
-  width: 400px;
+  min-width: 400px;
   border: 1px solid #ababab;
   background: white;
   -moz-border-radius: 13px;

addons/web/static/src/css/base.sass

@@ -964,7 +964,7 @@ $sheet-padding: 16px
                 > .oe_view_manager_body
                     position: absolute
                     overflow: auto
-                    top: 90px
+                    top: 91px
                     bottom: 0
                     left: 0
                     right: 0
@@ -1161,7 +1161,7 @@ $sheet-padding: 16px
         float: right
         padding: 1px 0
         line-height: 18px
-        width: 400px
+        min-width: 400px
         border: 1px solid #ababab
         background: white
         @include radius(13px)