Fix HasCargo#can_accept? to validate entity is alive
Add #alive? method to Station/Loot that always returns true

Compatibility fix, most likely station at the very least will
incorporate hp in the future
Stop entity movement when in is destroyed

Resolves a FIXME in the manufactured subsystem
Invalidate entity related commands when entity is destroyed

Tidies operations up when a manufactured entity is destroyed
by introducing a registry command cleanup mechanism (currently
specified to the manu subsystem).

Commands related to an entity are detected / quick removed so
they aren't lingering (shouldn't be a problem if they get picked
up by the next command cycle before this has a chance to happen
as all commands will self-terminate if a related entity is not
alive)

Specs have been updated to test new functionality