Support storing DIPs via the storage service

Refs #6564
updating descriptive text

refs #6691
control: fix unar version dependency
Store AIP: handle AIPs without pointer files

This is needed to support uncompressed AIPs, which do not have
pointer files.

refs #6589
Package: add new compress_package instance method

This supports features such as downloading entire AIPs for
uncompressed AIPs.

Note that this currently only tarballs the file without performing
actual compression.
PackageResource: allow downloading uncompressed packages

refs #6589
Package: don't try to call methods on None pointer_file_location
Pointer file request: return 404 if no pointer file exists