Should Bucket.copy_blob be moved over to Blob?

[dhermes]

/cc @tseaver

[tseaver]

My inclination is to treat copy and rename operations as more closely associated with "containers" than with "items".

[dhermes]

So then we should move Blob.rename to Bucket?

[dhermes]

@tseaver Bump

[tseaver]

I'd be fine with having Blob.rename move to Bucket.rename_blob.