Unclear org-icompleting-read interface

[Oleh Krehel <ohwoeowho@gmail.com>]

Hi all,

The current `org-icompleting-read' is defined as taking only `&rest
args', which can be as many as 8, all of them without a name.

I propose to update the definition to:

    (cl-defun org-icompleting-read (prompt collection
                                    &key predicate require-match
                                      initial-input hist def inherit-input-method)
      ;; ...
      )

Let me know if you like the idea. If so, there are 43 calls to
`org-icompleting-read' in the source that need to be updated. Some of
them should as they are, since usually only the first two arguments are
used.

This change would make the calls to `org-icompleting-read' much easier
to read.

regards,
Oleh