Tweaks to the sly-stickers contrib

* sly-stickers.el (sly-stickers-empty-face): New face.
(sly-stickers-recordings-face): Renamed from `sly-stickers-lit-face'
(sly-stickers-mode-map): Simplify keymap.
(sly-stickers--arm-sticker): Use `sly-stickers--last-values-list'
(sly-stickers--disarm-sticker): Don't remhash here.
(sly-stickers--populate-sticker): Adapt to new fetched values.
(sly-stickers--mark-empty-sticker): New function.
(sly-stickers--bring-out-yer-dead): Actually bring out the dead.
(sly-stickers--delete): Leave in hash table.
(sly-stickers-dwim): Simplify.
(sly-stickers-fetch): Adapt to new protocol.

* slynk-stickers.lisp (sticker): New class.
(record): No need for so many gensyms.
(check-stickers): Return less info.
(inspect-sticker-values): Sticker is now its own class.