Version Selector (#4386)

* Show current version of docs in nav

* Branch in edit link

* WIP version selector

* An actual working but not pretty version dropdown

* update URLs for versions

v1.7: https://kubernetes.io/docs/home/
v1.6: https://v1-6.docs.kubernetes.io/docs/home/
v1.5: https://v1-5.docs.kubernetes.io/docs/home/
v1.4: https://v1-4.docs.kubernetes.io/docs/home/

* fix v1.4 and v1.5 paths

* Tidier drop downs

* Make font visible always

* Make background match main nav always

* change to major.minor version number

* show only major.minor version in drop down list

* switch from githubbranch to docsbranch

* update githubbranch

* update githubbranch values

* Border radius for bottom of dropdown

* Tabs are hard

_includes/header.html

@@ -10,6 +10,17 @@
             <li><a href="/partners/">Partners</a></li>
             <li><a href="/community/">Community</a></li>
             <li><a href="/case-studies/">Case Studies</a></li>
+            <li>
+                <a href="#">
+                    {{page.version}} <span class="ui-icon ui-icon-carat-1-s"></span>
+                </a>
+                <ul>
+                {% for version in page.versions %}
+                  <li><a href="{{ version.url }}">{{ version.version }}</a></li>
+                {% endfor %}
+                </ul>
+              </li>
+            </li>
         </ul>
         <!-- <a href="/docs/home" class="button" id="viewDocs" data-auto-burger-exclude>View Documentation</a> -->
         <a href="/docs/tutorials/kubernetes-basics/" class="button" id="tryKubernetes" data-auto-burger-exclude>Try Kubernetes</a>