[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/component-animations.less

@@ -0,0 +1,33 @@
+//
+// Component animations
+// --------------------------------------------------
+
+// Heads up!
+//
+// We don't use the `.opacity()` mixin here since it causes a bug with text
+// fields in IE7-8. Source: https://github.com/twbs/bootstrap/pull/3552.
+
+.fade {
+  opacity: 0;
+  .transition(opacity .15s linear);
+  &.in {
+    opacity: 1;
+  }
+}
+
+.collapse {
+  display: none;
+
+  &.in      { display: block; }
+  tr&.in    { display: table-row; }
+  tbody&.in { display: table-row-group; }
+}
+
+.collapsing {
+  position: relative;
+  height: 0;
+  overflow: hidden;
+  .transition-property(~"height, visibility");
+  .transition-duration(.35s);
+  .transition-timing-function(ease);
+}