Support get/set on storage service properties for API version 2013-08-15

Support get/set on storage service properties for version 2013-08-15 by adding serialization for new features and fixing the header version at  2013-08-15. Doesn't support any other version of the API for those methods. Breaks any dependencies on existence of Storage Service Metrics (as it switched to hour and minute). Not well tested.

This is not ready to be merged but I'm creating this pull request as a way to discuss this feature and to allow people who **really need** cors to use it.

Fixes #128

Related documentation [Set Blob Service Properties](http://msdn.microsoft.com/en-us/library/azure/hh452235.aspx)