Make Pants::Binary use PostgreSQL Large Objects

[hmans]

...as they may be faster than bytea.

http://www.postgresql.org/docs/9.4/static/largeobjects.html https://gist.github.com/hmans/cf18d182c51fb9191df6

Tasks:

• [ ] Remove payload from Pants::Binary
• [ ] Add a new oid column
• [ ] Add a virtual attribute that will, on save, be saved into a LO, storing the OID in the model
• [ ] Adapt Dragonfly datastore code

[hmans]

ActiveRecord doesn't like oid columns. :(

[hmans]

Closing for the time being. If ActiveRecord ever starts supporting oid columns natively, we can reconsider.