Updating the header for login/logout

I changed the header in order to show only the gitlab sign-in/login
button when the user isn't authenticated and logout button when he is.
Signed-off-by: Matthieu Berjon <matthieu.berjon@inria.fr>

django/allgo/templates/partials/_header.html

-{% load static activelink %}
+{% load static activelink socialaccount%}
 
 <header class="container-fluid">
   <div class="container">
@@ -21,13 +21,14 @@
 
         <ul class="navbar-nav ml-auto">
           {% if not user.is_authenticated %}
-          <li class="nav-item 
-            {% is_active request 'account_login' %}">
-            <a class="nav-link" href="{% url 'account_login' %}">Sign in</a>
-          </li>
-          <li class="nav-item nav-link disabled">or</li>
-          <li class="nav-item {% is_active request 'account_signup' %}">
-            <a class="nav-link" href="{% url 'account_signup' %}">Sign up</a>
+          <li class="nav-item">
+            {% get_providers as socialaccount_providers %}
+            {% if socialaccount_providers %}
+            {% for account in socialaccount_providers %}
+            <a href="{% provider_login_url account.id %}"
+              class="btn btn-primary {{ account.id }} text-center ">Log in with Gitlab</a>
+            {% endfor %}
+            {% endif %}
           </li>
           {% else %}
           <li class="nav-item {% is_active request 'user_webapp_list' 'webapp_update' 'webapp_creation' 'webapp_sandbox_panel' %}">
@@ -45,7 +46,7 @@
             <a class="nav-link" href="{% url 'main:user_detail' %}"><i class="fas fa-user"></i> Profile</a>
           </li>
           <li class="nav-item {% is_active request 'account_logout' %}">
-            <a class="nav-link" href="{% url 'account_logout' %}"><i class="fas fa-sign-out-alt"></i> Sign out</a>
+            <a class="btn btn-primary" href="{% url 'account_logout' %}"><i class="fas fa-sign-out-alt"></i> Sign out</a>
           </li>
           {% endif %}
         </ul>