zshrc: Keep .zshrc.local in $HOME/.zshrc_local

This is consistent with other local config files.
setup: No special case for skiplist.
setup: Reindent
setup: Fix symlinks inside symlinks.

When you ran it twice, it would create a symlink to the dir inside
whatever the symlinked directory was.
setup: Support initial seeding of files.

This is good for files that don't support local includes, but where a
new setup should at least have some basic configuration that you can
tweak (e.g. .ssh/config)
Remove gitignore for .zshrc.local
Add seed for .ssh/config.