This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
This refactors handling of s3 so it can be specified via GlobalSetting
This means that in a multisite environment you can configure s3 uploads
without actual sites knowing credentials in s3
It is a critical setting for situations where assets are mirrored to s3.
