Move setPublicationName to data package

Dryad Data Files do not actually have publicationName metadata in the
archive, so the setPublicationName has been moved into
DryadDataPackage. Tests fail.
Implementations of getDataPackage, getDataFiles

Both use dc.relation metadata
Methods to assign files to packages

Needs tests
Update tests - no publicationName on files

Tests will fail since extractors don’t know the package->file hierarchy
and no identifiers are assigned.
Creating packages or files create an identifier
Tests for creating identifiers
Tests for new data package methods
Fix buggy test
Startup dspace kernel in ContextUnitTest
Refactor up File/package link for compatibility

DOI Identifier provider requires the file to be part of a package
before assigning an identifier. Makes sense, since the file IDs are
derived from package IDs
Update tests - DryadDataFile() reqs package
Prevent missing crosswalk from breaking tests
Implement equals and hashCode in DryadObject

Allows objects to be compared, and set membership testing
Fixes tests of packages containing files
Update dataFiles/dataPackage vars when changing
Fix file/package removal bugs

Now all org.datadryad.api tests pass
Update Package/File creation in stat tests
Support for getting related items by collection
Fixes in base class for counting files by journal
Prevent treating other items as DryadDataPackage
Refactor EmbargoedDataFileCount with filter()