After pasting commits once, we hide the cherry-picking status (as if it had been
reset), and no longer paint the copied commits with blue hashes; however, we
still allow pasting them again. This can be useful e.g. to backport a bugfix to
multiple major version release branches.
We've been sometimes using lo and sometimes using my slices package, and we need to pick one
for consistency. Lo is more extensive and better maintained so we're going with that.
My slices package was a superset of go's own slices package so in some places I've just used
the official one (the methods were just wrappers anyway).
I've also moved the remaining methods into the utils package.
