Fix breakage due to outline-invisible-p defn change in emacs 26+

Fix breakage due to outline-invisible-p defn change in emacs 26+

* lisp/org.el (org-invisible-p): New function.  Restore the behavior
of outline-invisible-p prior to the following commint on emacs master
<http://git.savannah.gnu.org/cgit/emacs.git/commit/?id=9cc59ffbbb2f20fbbf1c72d2e0c9dc47c7906a99>.

* lisp/org.el (org-cycle-internal-local)
(org-clean-visibility-after-subtree-move, org-goto)
(org-get-location, org-move-subtree-down, org-copy-subtree)
(org-paste-subtree, org-next-link, org-mark-ring-goto)
(org-todo, org-deadline, org-schedule, org-set-tags)
(org-truely-invisible-p, org-invisible-p2)
(org-forward-heading-same-level, org-forward-paragraph)
(org-backward-paragraph, org-down-element)
(org-bookmark-jump-unhide, org-mark-jump-unhide):
* lisp/org-list.el (org-insert-item):
* lisp/org-crypt.el (org-encrypt-entry, org-decrypt-entry):
* lisp/org-clock.el (org-clock-load):
* lisp/org-archive.el (org-archive-subtree)
(org-archive-to-archive-sibling, org-toggle-archive-tag)
(org-archive-set-tag):
* contrib/lisp/org-drill.el (org-drill-hide-subheadings-if): Use
org-invisible-p instead of outline-invisible-p.

Reference:
<http://lists.gnu.org/archive/html/emacs-orgmode/2017-06/msg00230.html>