Added a List method for listing the contents of a FileStore.

Filestore currently supports read write and delete to a file store, this request is to ad support for listing objects thats have already been added to a given directory
It is possible to dig into the exception and find out what can go wrong. Any Client/Service exceptions need to be rethrown as PersistenceResourceFailureException

PersistenceResourceFailureException as well as PersistenceException should probably live in:

com.clicktravel.cheddar.infrastructure.persistence.exception (not absence of "database")