Fix Django 1.10 and 2.0 compatibility

- Handle "aggregate_select" deprecated method from django.db.sql.query.Query.
- Import "reverse" compatible with both versions 1.10 and 2.0.

django_tablib/admin/__init__.py

@@ -5,7 +5,14 @@
 import django
 from distutils.version import LooseVersion
 from django.contrib import admin
-from django.core.urlresolvers import reverse
+
+try:
+    # Django <= 1.10
+    from django.core.urlresolvers import reverse
+except ImportError:
+    # Django >= 2.0
+    from django.urls import reverse
+
 from django.http import Http404
 
 

django_tablib/datasets.py

@@ -20,7 +20,10 @@ def __init__(self, queryset, headers=None, encoding='utf-8'):
                 # django < 1.9
                 field_names = v_qs.field_names
             headers.extend(field_names)
-            headers.extend(v_qs.query.aggregate_select)
+
+            if hasattr(v_qs.query, 'aggregate_select'):
+                # Django < 1.10
+                headers.extend(v_qs.query.aggregate_select)
 
             self.header_list = headers
             self.attr_list = headers