org-mac-link.el: Handle links to/from Adobe Acrobat

org-mac-link.el: Handle links to/from Adobe Acrobat

Add new link type "acrobat" to grab links to documents open in Adobe
Acrobat application.

* contrib/lisp/org-mac-link.el (org-mac-acrobat-open): Open Adobe
  Acrobat document pointed to by a link.
* contrib/lisp/org-mac-link.el (org-mac-as-get-acrobat-page-link):
  Invoke applescript to generate a link to an open and active Adobe
  Acrobat document.
* contrib/lisp/org-mac-link.el (org-mac-acrobat-get-page,
  org-mac-acrobat-insert-page): methods used when an Adobe Acrobat link
  grab request is issued or a link is clicked in an org document.
* contrib/lisp/org-mac-link.el (org-mac-grab-Acrobat-app-p): predicate
  that enables grabbing Adobe Acrobat links.

Signed-off-by: Alan Schmitt <alan.schmitt@polytechnique.org>