Added GoogleStorageMixin.
Added GoogleStorageMixin.

This is a straight copy/paste of the existing S3BotoStorageMixin, but
it allows the use of the django-google-storage package.
ryneeverett/filebrowser-safe,ryneeverett/filebrowser-safe,fawx/filebrowser-safe,fawx/filebrowser-safe,fawx/filebrowser-safe,ryneeverett/filebrowser-safe,ryneeverett/filebrowser-safe