Add swiper-query-replace

* ivy.el (ivy-read): Update signature - a keymap is also accepted and
  the argument order has changed.
  The keymap is composed with `ivy-minibuffer-map'.
  Update for `ivy--action'.
(ivy--action): New defvar. If a function sets it, `ivy-read' will call it.

* swiper.el (swiper-map): New defvar.
(swiper-query-replace): New defun.
(swiper--ivy): Use swiper-map in the call to `ivy-read'.

* counsel.el (couns-git): Fix one empty candidate.