Change raneftable return type again - i.e. undo #634 a bit

[dmbates]

In #634 we changed the output type of raneftables to be a NamedTuple of DictTables. That is proving to be awkward. I thought it would be common to want to access rows of these tables by the String or Symbol of the grouping factor level but that doesn't seem to be the case. Often we want to sort them by the value of the random effects themselves and I have found that the Dictionaries.Dictionary form of the table and the fact that a column extracted from the table is itself a Dictionary and not a Vector makes working with them cumbersome. And I wouldn't want to have to explain the various contortions in the code needed to do this.

I will create a PR to change the DictTable to a TypedTables.Table.

[palday]

I'm glad we added the note about what the API promise is. 😄 But yes we should make the return value as directly useable as possible. 👍