Correcting 'Invalid template exception' in Frontend.php
Refactored content link generation

Content link generation separated into multiple functions for clarity
Bolt\Content::link no longer throws an exception for unroutable content
Updated backend & sitemap templates for unroutable content
Revert "Correcting 'Invalid template exception' in Frontend.php"

This reverts commit 9cc2dee2fcf3493fe8c17b31bfc0d3184eca67e7 and corrects as explained in bolt/bolt#918
Removed unnecessary pass/return by reference
Merge pull request #918 from rixbeck/master

Correcting 'Invalid template exception' in Frontend.php
Merge pull request #919 from jcracknell/contentlink-refactor

Refactored content link generation
Initial commit of new Authenticate extension.