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

_sass/_base.sass

@@ -258,12 +258,40 @@ ul.global-nav
 				left: 0
 				background: #fff
 
+		ul
+			display: none
+			position: fixed
+			top: 40px
+			text-align: left
+
+			li
+				display: block
+				height: 28px
+
+				a
+					background: $dark-grey
+					color: #fff
+					padding: 7px
+
+			li:last-child
+				a
+					border-radius: 7px
+
+	li:hover
+		ul
+			display: block
+
 
 .flip-nav ul.global-nav li a,
 .open-nav ul.global-nav li a,
-	color: #333
+	color: $dark-grey
+
+.flip-nav ul.global-nav li ul li a,
+	background: #fff
+	color: $dark-grey
 
 .flip-nav ul.global-nav li a.active:after,
+.flip-nav ul.global-nav li ul li a.active:after,
 .open-nav ul.global-nav li a.active:after,
 
 	background: $blue