Remove TODO comment as authentication was added.
Add initial stub class for SystemMetadata.

Also add associated test.  Eventually this will be replaced with a code-generated version of the object that is generated with XMLSchema, but due to current  issues with XMLSchema it is unable to parse the dataoneTypes.xsd schema file.
Fix Node documentation for parseCapabilities method.
Initial parsing function for xml system metadata.  Working on test now.
Added parsing for SystemMetadata documents, and start of a test for the class.
Add SystemMetadata class to package metadata.
Refactor parseSystemMetadata to be a S4 method.
Initial work on a constructor to parse xml SystemMetadata.
Updated slot documentation for SystemMetadata class.