Spider tweaks

Reworks the spider "fur" to something marginally more realistic, links the chitin and fur branches, and adjusts a dream now that spiders sleep in webs.

Fixes #10616.
Incorporates BevapDin's fix and corrects a few debuffs I missed.
Gives Insect the compound-eyes mutation too.
Removes compound eyes from spiders.

Apparently this one was mis-located since Whales-era.  Better late than never.
Merge pull request #10623 from KA101/muts

Spider tweaks