Update app to the app registry API

apps/navigation/widgets.py

@@ -7,6 +7,8 @@ from django.template.defaultfilters import capfirst
 from django.core.exceptions import PermissionDenied
 from django.template import RequestContext
 
+from icons.api import get_icon_name, get_sprite_name
+from icons.literals import ERROR
 from permissions.models import Permission
 
 
@@ -27,7 +29,7 @@ def render_widget(request, link):
     if resolved_link:
         return mark_safe(u'<a style="text-decoration:none; margin-right: 10px;" href="%(url)s"><button style="vertical-align: top; padding: 1px; width: 110px; height: 100px; margin: 10px;"><img src="%(static_url)simages/icons/%(icon)s" alt="%(image_alt)s" /><p style="margin: 0px 0px 0px 0px;">%(string)s</p></button></a>' % {
             'url': resolved_link.url,
-            'icon': getattr(resolved_link, 'icon', 'link_button.png'),
+            'icon': get_icon_name(getattr(resolved_link, 'icon', ERROR)),
             'static_url': settings.STATIC_URL,
             'string': capfirst(resolved_link.text),
             'image_alt': _(u'icon'),