Make lookupHelper container aware.

* Adds functionality to lookup components from the container (replaces ember-handlebars `resolveHelper`).
* Moves `ember-handlebars/component_lookup` to `ember-views/component_lookup` (it isn't really related to handlebars at all).
* Pass the `view` into `lookupHelper` (need it for container lookups).
* Remove `lookupHelper` from `hooks` (it is just looked up).

This is needed for the `{{unbound}}` helper, and for automatic component lookup from templates.
Updated to use `env.dom`.