Move Piwik provisioning into a Celery task.
Add Piwik tasks to source control.
Move storage setup into separate Celery import.
Defer Celery tasks until request teardown.
Show statistics on private nodes.
Revert preprocess request in base test cases.
Move Celery setup and teardown into signals.
Merge branch 'hotfix/0.21.9'
Merge branch 'hotfix/0.21.10'
Pass original file name to preserve file extensions.
Begin endpoints for glacier metadata.

Tests to follow.
Merge branch 'develop' of https://github.com/CenterForOpenScience/osf.io into feature/async-piwik

Conflicts:
	framework/tasks/__init__.py
Merge branch 'feature/async-piwik' into develop
Merge branch 'hotfix/0.21.11'
Merge branch 'hotfix/0.21.11' into develop
Update changelog
Test metadata logic in models and views.
Merge branch 'develop' of https://github.com/CenterForOpenScience/osf.io into feature/osf-storage-glacier
Default SENTRY_DSN to None

...to avoid instantiating a Sentry client in local environments

[skip ci]
Updates Google Analytics code snippet to implement Universal Analytics as well as allow for cross-tracking between OSF and COS domains.