add partial frontend

core/frontend/widgets/err_banner.jinja

@@ -0,0 +1,14 @@
+{% if error > 0 %}
+<div class="err-banner">
+<h3>Error</h3>
+{% if error == 1 %}
+Card not registered, or wrong password
+{% elif error == 2 %}
+Missing or malformed access code
+{% elif error == 3 %}
+Failed to create user
+{% else %}
+An unknown error occoured
+{% endif %}
+</div>
+{% endif %}