Template cleanup (#6421)

* Clean up & comment base templates

* Clean up login template & form

* Use SVG file for NetBox logo

* Simplify breadcrumbs

* Merge changelog.html into home.html

* Rename title_container block to header

* Move breadcrumbs block to object.html

* Attach names to endblock template tags

* Reorganize root-level templates into base/ and inc/

* Remove obsolete reference to Bootstrap 3.4.1

netbox/templates/exceptions/permission_error.html

@@ -9,4 +9,4 @@
         media root is <code>{{ settings.MEDIA_ROOT }}</code>. Ensure that the user NetBox runs as has access to write
         files to all locations within this path.
     </p>
-{% endblock %}
+{% endblock message %}