Add search field to navbar. Advances #77.

ticdesk/templates/ticdesk/base.html

@@ -23,6 +23,10 @@
   <div class="collapse navbar-collapse" id="navbar-main">
    <ul class="nav navbar-nav ml-auto">
     {% if user.is_authenticated %}
+     <form class="form-inline">
+      <input class="form-control mr-sm-2" type="search" placeholder="Benutzername" aria-label="Search">
+      <button class="btn btn-outline-success my-2 my-sm-0" type="submit">Suchen</button>
+     </form>
      <li class="nav-item dropdown">
       <a class="nav-link dropdown-toggle" data-toggle="dropdown" id="navbarDropdown" aria-expanded="false" role="button" aria-haspopup="true" href="#">
        {% blocktrans %}Veranstaltungen{% endblocktrans %}