Update pointer file in reingest

refs #6488

Update checksum and add another compression event after reingest.
Compression event information is stubbed out.

Squash with 'Stub out finish_reingest AIP'?
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.
Update compress_package for get_local_path changes
compress_package accepts compression algorithm parameter

Add compression constants to Package class for algorithms supported by
Archivematica.  Update compress_package to take a parameter for which
compression algorithm to run and use that.