Make Application model truly 'swappable'

This also introduces a new non-namespaced setting
OAUTH2_PROVIDER_APPLICATION_MODEL.

Author: oliviersels

oauth2_provider/models.py

@@ -109,6 +109,9 @@ def __str__(self):
 class Application(AbstractApplication):
     pass
 
+# Add swappable like this to not break django 1.4 compatibility
+Application._meta.swappable = 'OAUTH2_PROVIDER_APPLICATION_MODEL'
+
 
 @python_2_unicode_compatible
 class Grant(models.Model):

oauth2_provider/settings.py

@@ -34,7 +34,7 @@
     'WRITE_SCOPE': 'write',
     'AUTHORIZATION_CODE_EXPIRE_SECONDS': 60,
     'ACCESS_TOKEN_EXPIRE_SECONDS': 36000,
-    'APPLICATION_MODEL': 'oauth2_provider.Application',
+    'APPLICATION_MODEL': getattr(settings, 'OAUTH2_PROVIDER_APPLICATION_MODEL', 'oauth2_provider.Application'),
 
     # Special settings that will be evaluated at runtime
     '_SCOPES': [],