[Idea] Display columns in column-order as they are sorted in the source data.frame

Using the same example as available in the `README` (`file.show(app)`) . The app looks like this

Notice that the column in the dropdown has the order `height`, `is_droid`, `mass` but the order that we pass in choices is `choices = c("height", "mass", "is_droid")`. The column in the dropdown sorts the name and follows an alphabetical order ignoring the order that is passed in `choices`.

Can this be fixed to make the columns in the dropdown and `choices` consistent? Similarly, when no value of `choices` is passed meaning all the columns are part of filter I would expect the column order in dropdown same as that present in table.