Allow binaries to be ignored during the backup/restore process

During backup & restore ModeShape currently not only backups & restores binary values, but also keeps track of incoming binary changes that take place during the backup process. Since binary files are always referenced by documents using the SHA1 of the binary value, it may not always be necessary/desired to perform full binary backup/restore.
We should enhance the backup/restore code to allow ignoring binary values, resulting in effect only in the backup & restore of documents.