condition on sigup

added a if condition to check the variable SECURITY_REGISTERABLE value.

invenio_theme_tugraz/templates/invenio_theme_tugraz/accounts/header_login.html

@@ -1,11 +1,14 @@
 {%- if config.ACCOUNTS %}
 
 {%- if not current_user.is_authenticated %}
+
+{%- if config.SECURITY_REGISTERABLE %}
 <div class="short-menu-right-button">
     <a href="{{ url_for('security.register') }}">
         <i class="user plus icon circular"></i> Sign Up
     </a>
 </div>
+   {%- endif %}
 
 <div class="short-menu-right-button">
     <a href="{{url_for_security('login', next=request.path)}}" style="text-decoration:none">
@@ -30,4 +33,4 @@
 
 {%- endif %}
 {%- endif %}
-{%- endif %}
+{%- endif %}