[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/nav-vertical-align.less

@@ -0,0 +1,9 @@
+// Navbar vertical align
+//
+// Vertically center elements in the navbar.
+// Example: an element has a height of 30px, so write out `.navbar-vertical-align(30px);` to calculate the appropriate top margin.
+
+.navbar-vertical-align(@element-height) {
+  margin-top: ((@navbar-height - @element-height) / 2);
+  margin-bottom: ((@navbar-height - @element-height) / 2);
+}