[FIX] web: unbreak tree view

The do_show and do_hide methods did not call their _super, which is bad.
Also, add an icon for the poor treeview.

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

@@ -528,7 +528,7 @@
   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;
@@ -1048,6 +1048,9 @@
 .openerp .oe-view-manager-header .oe-view-manager-switch .oe-vm-switch-pivot:before {
   content: "";
 }
+.openerp .oe-view-manager-header .oe-view-manager-switch .oe-vm-switch-tree:before {
+  content: "";
+}
 .openerp .oe-view-manager-header .oe-view-manager-buttons {
   display: inline-block;
 }

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

@@ -897,6 +897,8 @@ $sheet-padding: 16px
                 content: "\f0ae"
             .oe-vm-switch-pivot:before
                 content: "\f0ce"
+            .oe-vm-switch-tree:before
+                content: "\f036"
         .oe-view-manager-buttons
             display: inline-block
             > div

addons/web/static/src/js/view_tree.js

@@ -258,11 +258,13 @@ instance.web.TreeView = instance.web.View.extend(/** @lends instance.web.TreeVie
 
     do_show: function () {
         this.$el.show();
+        this._super();
     },
 
     do_hide: function () {
         this.$el.hide();
         this.hidden = true;
+        this._super();
     }
 });
 })();