Update Portal styles & templates

Officially renames it the "XRP Ledger Developer Portal" and
adapts the Ripple Client Portal templates to the XRP Dev Portal:

- Table-of-Contents-like landing page
- Accordion-style side nav except on landing page
- Breadcrumbs except on landing page
- floating (right-side) in-page nav on doc pages
- Adds "Edit on GitHub" link
- Slight modifications to API tool styles

tool/template-footer.html

@@ -3,7 +3,7 @@
         <div class="row">
        		<div class="col-sm-12 absolute_bottom_footer">
        			<div class="col-sm-8">
-                    <span>&copy; 2013 - 2017 Ripple Labs, Inc. All Rights Reserved.</span>
+                    <span>&copy; 2013 - 2018 Ripple. All Rights Reserved.</span>
                     <span><a href="/terms-of-use/">Terms</a></span>
                     <span><a href="/privacy-policy/">Privacy</a></span>
                 </div>
@@ -12,3 +12,7 @@
         </div><!-- /.row -->
     </div><!-- /.container -->
 </footer>
+
+<!-- Jump to top button -->
+<a href="#main_content_wrapper" class="jump-to-top btn btn-primary btn-lg" role="button" title="Jump to top of page">Top</span></a>
+<script type="text/javascript" src="assets/js/jump-to-top.js"></script>