Now that even Debian stable has picked up version 0.8, we can safely
make this a requirement, and remove a lot of old cruft.

This old version has been obsolete for many years - time to remove it.

Allow reusing Tag instances.

Avoid duplicating the tag.

If no state file is configured, don't chek for state changes.

This destroys data inside PcmDsd and other attributes.  It was once
necessary, but is not anymore.