Fix overlay priority calculation in sly-stickers

* sly-stickers.el (sly-stickers--decrease-prio)
(sly-stickers--increase-prio): Don't recurse.
Preparatory work for new `sly-stickers-fetch-and-replay' command

* contrib/sly-stickers.el (sly-stickers-mode-map): Change
`sly-sticker-dwim' binding yet again to C-c C-s C-s to free up C-c
C-s prefix for other sticker-related operations. Bind C-c C-s C-r
to unimplemented `sly-stickers-fetch-and-replay'.
(sly-stickers-fetch-all-and-forget): Renamed from
`sly-stickers-fetch'.
(sly-stickers-fetch-and-replay): New function.

* contrib/slynk-stickers.lisp (call-with-sticker-recording): New helper function.
(record): Use CALL-WITH-STICKER-RECORDING
(check-and-forget): Renamed from CHECK-STICKERS.