truncate error description in admin

Also removes old conditional imports

django_q/models.py

@@ -1,8 +1,7 @@
 from django import get_version
-try:
-    from django.urls import reverse
-except ImportError: # Django < 1.10
-    from django.core.urlresolvers import reverse
+from django.template.defaultfilters import truncatechars
+
+from django.urls import reverse
 from django.utils.html import format_html
 from django.utils.translation import ugettext_lazy as _
 from django.db import models
@@ -82,6 +81,10 @@ class Task(models.Model):
     def time_taken(self):
         return (self.stopped - self.started).total_seconds()
 
+    @property
+    def short_result(self):
+        return truncatechars(self.result, 100)
+
     def __unicode__(self):
         return u'{}'.format(self.name or self.id)