chore(plainui): list self-organized-project in plus button

src/plainui/jinja2/plainui/components/nav.html.j2

@@ -109,12 +109,13 @@
               Assembly
             </a>
           </li>
-          <!--li>
-          <a class="dropdown-item" href="#" disabled>
+          <li>
+            <a class="dropdown-item{% if conf.has_ended %}disabled{% endif %}"
+               href="{{ hub_absolute('backoffice:so-create-project') }}">
               <i class="bi bi-hammer"></i>
-              Projekt
+              Self-organised-project
             </a>
-      </li -->
+          </li>
           <li>
             <a class="dropdown-item {% if conf.has_ended %}disabled{% endif %}"
                href="{{ hub_absolute('backoffice:sos-create') }}">