Make profile Inherit djangoldp.Model

Closes #2 (closed)

djangoldp_profile/models.py

 from django.conf import settings
+from django.core.urlresolvers import reverse_lazy
 from django.db import models
 from django.db.models.signals import post_save
 from django.dispatch import receiver
-from django.core.urlresolvers import reverse_lazy
+
+from djangoldp.models import Model
 
 
-class Profile(models.Model):
+class Profile(Model):
     user = models.OneToOneField(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
     available = models.NullBooleanField(blank=True)
     bio = models.CharField(max_length=150, blank=True)
@@ -27,10 +29,6 @@ class Profile(models.Model):
         )
         depth = 0
 
-    def get_absolute_url(self):
-        return reverse_lazy('profile-detail', kwargs={'pk': self.pk})
-
-
     def __str__(self):
         return '{} ({})'.format(self.user.get_full_name(), self.user.username)