Expose the log_id of the deletion log entry in the action=delete API

Expose the log_id of the deletion log entry in the action=delete API

This entails some refactoring to actually surface the log_id all the way
up:

* Made doDeleteArticleReal() return a Status object rather than a
  constant, and put the log_id in $status->value. This Status object is
  also passed to the ArticleDelete hook.
* Kept doDeleteArticle() the same for extension compatibility.
* Switched all core callers of doDeleteArticle() to
  doDeleteArticleReal() and surfaced the error message from the Status
  if appropriate, rather than hardcoding 'cannotdelete' all over the
  place.
* Exposed the log_id in ApiDelete
* Add 'delete-hook-aborted' message for when a hook aborts the deletion
  but does not provide an error message. Previously this just caused the
  'cannotdelete' message to appear.

Change-Id: Ia6415b390d5d4172ce96667f46ccdba2be02461f