MAINT: Use `Type` instead of `DottedObjectName` Log{in,out}Handler.
MAINT: Remove unused imports.

I was in the neighborhood...
DEV: Set `klass=object` for Log{in,out}Handler.

It seems plausible that people will implement custom handlers that
aren't subclasses of a known type.

Another possible option would be `IPythonHandler`, but even that feels
too restrictive.