New Packager class replacing Bagit libraries

[seesmith]

JIRA link https://www.jira.is.ed.ac.uk/browse/RSS022-11

Fix issues with BagIt Library so:

maintain empty directories in deposit without creating dot (hidden) files

maintain symbolic links (rather than resolving & duplicating)

maintain exact file and directory names, do not change filenames

handle the fact that there aren't checksums for empty directories and symbolic links
Checksums should not be created where there is no file, ie directories

Manifest to include symbolic links
Manifest to include empty directories

Ianthe notes:

Packager interface so can choose which to use

methods in Deposit:

Packager.createBag(bagDir);

Packager.addMetadata(bagDir, depositMetadata, vaultMetadata, fileTypeMetadata, externalMetadata);

Packager.extractMetadata(bagDir, metaDir);