fix: Make sure empty VERSION_EXTRA strings are ignored

Also updates built & removes unused optional features

src/web/templates/_layout.html.j2

@@ -18,7 +18,7 @@
     {%~ block footer ~%}
         <footer>
             <p>Powered by <a href="https://continuwuity.org">Continuwuity</a>
-                {%~ if let Some(version_info) = VERSION_EXTRA ~%}
+                {%~ if let Some(version_info) = self::version_tag() ~%}
                     {%~ if let Some(url) = GIT_REMOTE_COMMIT_URL.or(GIT_REMOTE_WEB_URL) ~%}
                         (<a href="{{ url }}">{{ version_info }}</a>)
                     {%~ else ~%}