[IMP] improve graph view layout and groupbys

* add a 'total' foldable button to allow the user to control the column
in pivot table view
* in the dropdown menu, add all fields from the model instead of only
those from the search view groupbys

addons/web_graph/static/src/css/graph.css

@@ -113,6 +113,7 @@ span.field-selection {
   border-radius: 3px;
 }
 
+
 .graph_widget .dropdown-menu li a, .graph_widget .dropdown-menu li a:hover, .graph_widget .dropdown-menu li a:focus {
   color: black;
   text-decoration: none;
@@ -124,3 +125,41 @@ th.measure_row {
   padding:0px 5px 0px 5px ;
   margin:0;
 }
+
+
+.dropdown-submenu {
+    position: relative;
+}
+
+.dropdown-submenu>.dropdown-menu {
+    top: 0;
+    left: 100%;
+    margin-top: -6px;
+    margin-left: -1px;
+    -webkit-border-radius: 0 6px 6px 6px;
+    -moz-border-radius: 0 6px 6px;
+    border-radius: 0 6px 6px 6px;
+}
+
+.dropdown-submenu:hover>.dropdown-menu {
+    display: block;
+}
+
+.dropdown-submenu>a:after {
+    display: block;
+    content: " ";
+    float: right;
+    width: 0;
+    height: 0;
+    border-color: transparent;
+    border-style: solid;
+    border-width: 5px 0 5px 5px;
+    border-left-color: #ccc;
+    margin-top: 5px;
+    margin-right: -10px;
+}
+
+.dropdown-submenu:hover>a:after {
+    border-left-color: #fff;
+}
+