Improved Swift header support

This PR needs to get into the 1.7.3 release and provides the changes necessary to address [JCLOUDS-547](https://issues.apache.org/jira/browse/JCLOUDS-547) where the static web headers were being set incorrectly on the CDN container. In general, Swift functionality is exposed via extended headers "x-*" and access to the headers is imperative.

Swift
- Added headers field to domain objects
- Added update method to ContainerApi
- Updated Option classes: `CreateContainerOptions` `PutOptions` `UpdateContainerOptions`
- Refactored CDN constants to `SwiftConstants`

CloudFiles
- Added deprecation for `CloudFilesApi.cdnApiInRegion()` -> `getCDNApiInRegion()`
- Updated Option classes and tests

Testing
- ran unit and live tests