Allow Crowbar attribs to be get and set easily via the API.

* Hey, Rails 4 has JSON as a native column type.  Use it for all the
  columns that we are saving JSON into.  This also gets rid of alot of
  my buggy special-casing that does the same thing.
* Add a schema attribute to the Attribs model.  If this is populated, it
  must make a valid Kwalify schema fragment, the attrib will be
  writable, and all writes that go through the attribute will be
  validated against the schema. The schema itself will be validated at
  barclamp import time.
* Strip out all of the special-case handling for hints.  They now only
  work with the hints field on the node object we are applying the hints
  to.  The only exception is the mac hint at node creation time, because
  Sledgehammer relies on it.
* Wire up attribs resources and routes for all objects that it is
  meaningful to get and set attribs through.
* Modify production.sh to use the new attrib finagling functionality.
* Update attrib-related documentation.