sphinx: Add support for multiple docs version

Enhance the sphinx experience/nagivation with:

* Remove the pointless looking parts of breadcrumb navigtation
* Add a document type switcher to the breadcrumb navigation
* Add a version selection switch to the breadcrumb navigation

(From yocto-docs rev: 1823624bdb9ea002d44c9e6d0fd4cd662bff36ad)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/_templates/breadcrumbs.html

@@ -0,0 +1,14 @@
+{% extends "!breadcrumbs.html" %}
+
+{% block breadcrumbs %}
+    <li>
+      <span class="doctype_switcher_placeholder">{{ doctype or 'single' }}</span>
+      <span class="version_switcher_placeholder">{{ release }}</span>
+    </li>
+    <li> &raquo;</li>
+    {% for doc in parents %}
+      <li><a href="{{ doc.link|e }}">{{ doc.title }}</a> &raquo;</li>
+    {% endfor %}
+    <li>{{ title }}</li>
+{% endblock %}
+

documentation/_templates/layout.html

@@ -0,0 +1,9 @@
+{% extends "!layout.html" %}
+
+{% set script_files = script_files + ['_static/switchers.js'] %}
+
+{% block extrabody %}
+<div id="outdated-warning" style="text-align: center; background-color: #FFBABA; color: #6A0E0E;">
+</div>
+{% endblock %}
+