Implement clock consistency check functionality for agenda

Implement clock consistency check functionality for agenda

* lisp/org-agenda.el (org-agenda-clock-consistency-checks): New option.
(org-agenda-list): Handle display change to clock check.
(org-agenda-get-progress): Show only clock entries if we are doing the
consistency check.
(org-agenda-show-clocking-issues): New function.
(org-agenda-check-clock-gap): New function.
(org-agenda-view-mode-dispatch): Offer consistency check.
(org-agenda-log-mode): Handle switch to clock only display.
(org-agenda-set-mode-name): Show lighter for Clockcheck.
* lisp/org.el (org-hh:mm-string-to-minutes): Accept an integer argument
and return it unchanged.
* doc/org.texi (Agenda commands): Document clock consistency checks.
* doc/orgcard.tex: Document key for clock consistency check.