Switch to side-by-side view

--- a/Allura/allura/model/__init__.py
+++ b/Allura/allura/model/__init__.py
@@ -22,6 +22,7 @@
 from .session import main_doc_session, main_orm_session
 from .session import project_doc_session, project_orm_session
 from .session import artifact_orm_session, repository_orm_session
+from .session import ArtifactSessionExtension
 
 import repo