FileSystem connector should support additional properties on nt:file and nt:folder

The FileSystem connector does not currently support properties other than those defined on the nt:file and nt:folder node types. The connector does define the CustomPropertiesFactory that allows an implementation class to define/handle additional properties, but this does require writing code and is not necessarily intuitive.

Since it is likely that applications want to store additional metadata on the files and folders exposed by the FileSystem connector, the connector should provide a way of doing this either by default or with a simple configuration setting. This means the connector would make use of a CustomPropertiesFactory implementation that stores the extra properties in an additional file (one per actual file or directory), and these metadata files would be filtered out so that they aren't represented in the JCR content with nt:file nodes.

Details would have to be worked out. For example, would each metadata file have the same name as the actual file or directory, but with either a prefix or a suffix? Are the properties stored in a serialized (binary) form, or perhaps in another form (e.g., JSON, XML, etc.) that is accessible outside of the connector? Certain properties, such as jcr:primaryType (if a subtype of nt:folder or nt:file) and jcr:mixinTypes would also need to be handled, and perhaps always stored if they don't match the values hard-coded into the connector.