LDP Updates

* Adding Link header declaring containers are DirectContainers
* Changing membership triples (now using ldp:membershipResource and ldp:hasMemberRelation)
* Adding support for OPTIONS method on nodes
* Adding Last-Modified header with create/update timestamp when nodes/datstreams are created/updated

Fixes:
* https://www.pivotaltracker.com/story/show/69469312
* https://www.pivotaltracker.com/story/show/69469226
* https://www.pivotaltracker.com/story/show/69467500
* https://www.pivotaltracker.com/story/show/68301562