[FIX] add scrollbar to filters menu if needed (web client)

the filters menu can quickly grow if the user adds many conditions.
Once it grows out of the screen, the lower buttons can not be reached
anymore.  This patch adds a vertical scrollbar to fix this issue.  It
has to use some javascript to update its max-height property.

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

@@ -532,7 +532,7 @@
   background-image: -webkit-radial-gradient(circle, #eee 0%, #ccc 40%, #bbb 100%);
   background-image: -moz-radial-gradient(#eee 0%, #ccc 40%, #bbb 100%);
   background-image: -ms-radial-gradient(#eee 0%, #ccc 40%, #bbb 100%);
-  background-image: radial-gradient(circle, #eeeeee 0%, #cccccc 40%, #bbbbbb 100%);
+  background-image: radial-gradient(circle, #eee 0%, #ccc 40%, #bbb 100%);
 }
 .openerp .oe_kanban_status_green {
   background: green;
@@ -1361,6 +1361,10 @@
 .openerp .oe-search-options .divider {
   display: none;
 }
+.openerp .oe-search-options .filters-menu {
+  overflow: auto;
+  overflow-x: hidden;
+}
 .openerp .oe-search-options .filters-menu .divider {
   display: list-item;
 }

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

@@ -1162,6 +1162,8 @@ $sheet-padding: 16px
         .divider
             display: none
         .filters-menu
+            overflow: auto
+            overflow-x: hidden
             .divider
                 display: list-item
         .closed-menu

addons/web/static/src/js/search.js

@@ -1441,6 +1441,10 @@ instance.web.search.FilterMenu = instance.web.Widget.extend({
             prop.$el.hide();
         });
     },
+    update_max_height: function () {
+        var max_height = $(window).height() - this.$menu[0].getBoundingClientRect().top - 10;
+        this.$menu.css('max-height', max_height);
+    },
     toggle_custom_filter_menu: function (is_open) {
         this.$add_filter
             .toggleClass('closed-menu', !is_open)
@@ -1450,6 +1454,7 @@ instance.web.search.FilterMenu = instance.web.Widget.extend({
             this.append_proposition();
         }
         this.$('.oe-filter-condition').toggle(is_open);
+        this.update_max_height();
     },
     append_proposition: function () {
         var self = this;
@@ -1458,6 +1463,7 @@ instance.web.search.FilterMenu = instance.web.Widget.extend({
             self.propositions.push(prop);
             prop.insertBefore(self.$add_filter_menu);
             self.$apply_filter.prop('disabled', false);
+            self.update_max_height();
             return prop;
         });
     },