Adding hasExternalContent/isExternalContentOf properties and IT for linking from repo object to federated filesystem datastream
Add external federation properties store.

Resolves: https://www.pivotaltracker.com/story/show/71234576
Merge pull request #395 from fcrepo4/external-datastreams

External datastream pattern
Support POST/PUT requests with a Content-Location header instead of a request body

Resolves: https://www.pivotaltracker.com/story/show/72099626
Reject access to jcr:content from REST-API for NOT_FOUND (status 404).

Resolves: https://www.pivotaltracker.com/story/show/71412046
Split kernel and kernel-api packages
  fcrepo-kernel-api -> fcrepo-kernel
  fcrepo-kernel     -> fcrepo-kernel-impl

Resolves: https://www.pivotaltracker.com/story/show/70718582
Minor update: follow-on to kernel refactoring.
Add fedora:writable triple and disable HTML UI actions if it is false

Resolves: https://www.pivotaltracker.com/story/show/65899330