[IMP] all: new design to match the one on odoo.com

* upgrade to bootstrap 3.3.6

* new Header, port website LESS
  - Add the new header
  - Modify sub-header in order to handle “back” button and version
    switcher
  - Port website’s Less:
    * Use same variables’ names
    * Review fonts and colours in order to fit the new style

* add new footer

* Review and optimise JS code in order properly handle the new header,
  footer and card.top animations

* replace  banner images

_extensions/odoo/static/bootstrap-3.3.6/less/mixins/panels.less

@@ -0,0 +1,24 @@
+// Panels
+
+.panel-variant(@border; @heading-text-color; @heading-bg-color; @heading-border) {
+  border-color: @border;
+
+  & > .panel-heading {
+    color: @heading-text-color;
+    background-color: @heading-bg-color;
+    border-color: @heading-border;
+
+    + .panel-collapse > .panel-body {
+      border-top-color: @border;
+    }
+    .badge {
+      color: @heading-bg-color;
+      background-color: @heading-text-color;
+    }
+  }
+  & > .panel-footer {
+    + .panel-collapse > .panel-body {
+      border-bottom-color: @border;
+    }
+  }
+}