Consider removing the root slot, and making it implicit #258
Description
e.g. _ROOT_ or something.
The basic issue is that the slot is not used in the model itself, only outside fo it. So really there's no need to name it, and by explicitly naming it there is a chance of error due to typos etc.
On the bright side, this allows "multi-linkage" thingy where we start a model with a different t root slot each time.
One middle ground option: create a synthetic root slots by making a compound slot from all non-parented slots. Use only if there is no explicit slot specification.