Update templates to match new `using` usage
Disconnect CanJS Cacheable models to avoid event madness

* Basically, instead of instances directly containing other instances
  (either directly or in lists), instances now contains stubs, and lists
  of stubs.  This more accurately reflects the data coming down from the
  server, and avoids mass event propagation.  Since we're not actually
  using events emanating from sub-objects and list-objects, this is
  okay.
* Adds Observe.prototype.stub and Observe.List.prototype.stubs to
  generate the stub objects on compatible Observes and Model instances.
* Adds Observe.prototype.reify and Observe.List.prototype.reify to
  return the corresponding instance(s) for given stubs and lists of
  stubs.
* Adds CMS.Models.get_stub and CMS.Models.get_stubs to mimic
  CMS.Models.get_instance and CMS.Models.get_instances, but return
  stubs.
* Note: Attached instances will still be instantiated
  (can.Cacheable.model will still be called), but the source instance
  will only retain the stub.
* Note: This commit loses some of the optimizations we made inside
  can.Model.Cacheable.model -- these can (and should) be reinstated, but
  are less important, since unnecessary events are less catastrophically
  slow.

* Additional fixes:
    - Overrides can.Model.Cacheable.attr to not bork when passed an
      Observe instances.
    - Fixes `using` mustache helper to use `reify` correctly, but this
      required changing the signature/usage to only support keyword
      arguments.
Fix tree-node adding by inserting relative to classes

* In strange cases, options.$footer and options.$header would be present
  in active TreeView instances, but would point at detached elements.
  Thus, using insertBefore, etc, would insert new nodes detached from
  the DOM.
* To fix, add `.tree-footer` classes, and insert relative to
  `this.element.find('.tree-footer')`, which seems to always work.
Update Models to use `stub` and friends instead of `model`

* also removes some `serialize` methods and objects which were
  either problematic (the methods) or unnecessary (the objects) with
  the `stub` paradigm.