Accept any content entity, not only nodes

I wonder whether the configuration should happen at the field level rather than the bundle entity level. It would make this a lot easier in terms of the machinery needed to hook into core -- form alters, save hooks and so on.

It would also open up possibilities of being able to direct terms to different fields, e.g.

- terms found in body field 1 -> set in term field 1
- terms found in body field 2 -> set in term field 2