feat(aio): revise Docs page; docs version selector in sidenav

aio/src/styles/1-layouts/_sidenav.scss

@@ -169,3 +169,13 @@ aio-nav-menu.top-menu {
   }
 
 }
+
+// Angular version selector
+md-sidenav .doc-version {
+  padding: 10px;
+
+  &:hover {
+    text-shadow: 0 0 5px #ffffff;
+    background-color: $lightgray;
+  }
+}

aio/src/styles/2-modules/_card.scss

@@ -16,7 +16,7 @@
   &:hover {
     text-decoration: none;
 
-    h2 {
+    section {
       color: $blue;
     }
 
@@ -34,7 +34,7 @@
   }
 
 
-  h2 {
+  section {
     color: $darkgray;
     font-size: 20px;
     line-height: 24px;
@@ -69,4 +69,7 @@
       font-size: 13px;
     }
   }
-}
+  .card-footer.center {
+    text-align: center;
+  }
+}

aio/src/styles/2-modules/_contributor.scss

@@ -133,7 +133,7 @@ aio-contributor {
         padding: 16px 24px;
         transform:rotateY(180deg);
 
-        h3 {
+        section {
           display: none;
         }
 
@@ -168,7 +168,7 @@ aio-contributor {
     transition: all .2s ease-in-out;
     }
 
-  h3 {
+  section {
     font-size: 14px;
     font-weight: 500;
     padding: 8px;
@@ -188,4 +188,4 @@ aio-contributor {
     overflow: scroll;
     font-weight: 400;
   }
-}
+}