Introduce CLOCK_INTO_DRAWER property like the existing LOG_INTO_DRAWER

Introduce CLOCK_INTO_DRAWER property like the existing LOG_INTO_DRAWER

* lisp/org.el (defcustom org-log-into-drawer): correct typo
* lisp/org-clock.el: new function org-clock-into-drawer to change
  the location of clock events based on properties CLOCK_INTO_DRAWER
  or, as fallback, LOG_INTO_DRAWER, like it is already possible for
  state change logs.
* lisp/org-clock.el (org-clock-jump-to-current-clock): add statement
  to let clause to bind org-clock-into-drawer to result of function
  eval
* lisp/org-clock.el (org-clock-find-position): add statement
  to let clause to bind org-clock-into-drawer to result of function
  eval, change let to let* since the binding is used later in the
  same clause
* doc/org.texi: document that both CLOCK_INTO_DRAWER and
  LOG_INTO_DRAWER can be used to override the contents of variable
  org-clock-into-drawer (or if unset, org-log-into-drawer)
* doc/org.texi: @xref->@pxref