Add GMTUsage class to track x-gmt-usage header data
Add policy parameter support to copy_key().

- Similar to other API which add a key or a bucket to the S3 server,
  Allow the user to override the default canned-acl which is applied
  to the new key. This default policy override is only used if the
  preserve_acl parameter is False.
Added Cloudian Virtual Bucket Support
Add Cloudian group canned acl names.
Cloudian Custom: Validate the meta parameter for Cloudian usage.

The meta parameter is used to list meta data when listing
objects in the bucket.
Return the x-amz-restore header with GET KEY and fix provider prefix.

Currently x-amz-restore is only supported by HEAD KEY but GET KEY also
returns the header when it has been successfully restored and the
restored key is awaiting expiry. Fixed the provider 'x-amz-' prefix
part so that it's consistent with other standard headers. Previously,
it was hardcoded.

This patch is hard to automate a test for as transitioning to GLACIER
and restoring back from GLACIER both take time. This change has been
manually tested.