Break up DependencyModule's dual function of providing a "depend_on" DSL and "included" block DSL into separate modules. But, unify both approaches under AS::Concern.

This reverts commit 0cac68d3.

  * Removing the dependency on AD::Request and AD::Response
  * Moving the logic for the request and response object
    into a new module that is included by default.
  * Changing Renderer and Redirector to use self.headers,
    self.content_type, and self.status, which have very basic
    default implementations on AC::Http. When RackConvenience
    is included (which it is by default on AC::Base), the full
    Request/Response logic is used instead of the simple logic.