is there any plan to support sorting on calculated fields?

i.e,
1. if user collection contains two field `amt1` and `amt2`
2. using `columns: [{title: "toatalamt", data: 'total()'}]`, `totalamt` field doesn't exists in user collection.
3. and meter helper as below.
```
User.helpers({
total: function () {
return this.amt1 + this.amt2;
}
});
```
The sort icon doesn't appears on `totalamt` column

Start with the column configuration using data: 'total()' and the User.helpers total entry point, then trace how the table decides whether a column is sortable. Confirm the expected behavior for a calculated field and verify that the sort icon and ordering are consistent for the totalamt column.

Written by the indexing model from the issue text.