org-list: reorder file, rename functions, improve comments

org-list: reorder file, rename functions, improve comments

* lisp/ob.el (org-babel-result-end): apply renaming.
* lisp/org-exp.el (org-export-mark-list-properties): apply renaming.
* lisp/org-list.el (org-list-prevs-alist): renamed from
  org-list-struct-prev-alist.
(org-list-parents-alist): renamed from org-list-struct-parent-alist.
(org-list-write-struct): renamed from org-list-struct-fix-struct.
(org-list-parse-list, org-sort-list, org-list-indent-item-generic,
org-toggle-checkbox, org-update-checkbox-count, org-cycle-list-bullet,
org-list-repair, org-insert-item, org-move-item-up, org-move-item-up,
org-move-item-down, org-next-item, org-previous-item,
org-end-of-item-list, org-beginning-of-item-list, org-apply-on-list):
apply renaming.
(org-get-bullet): removed function, as it is not needed anymore.