Add a popup menu in the main menu which allows to quickly jump between projects.

* refactor out the common menu code from several base*.html classes into main-menu.html
  and put the raw links into a unordered list (which makes it easier to create dynamic
  menus as we cannot insert block items into inline items in strict mode)
* query the list of available projects on every request and set them for every template
  in Middleware.php
* make the popup menu pretty

src/IDF/Middleware.php

@@ -112,6 +112,7 @@ function IDF_Middleware_ContextPreProcessor($request)
         $c = array_merge($c, $request->rights);
     }
     $c['usherConfigured'] = Pluf::f("mtn_usher_conf", null) !== null;
+    $c['allProjects'] = IDF_Views::getProjects($request->user);
     return $c;
 }