ui.table format values from a column

[mattrunyon]

We should support reading the value for a format from a column. We could do this in a few ways

1. Check if all values are column names. If they are, add the column to always_fetch_columns
2. Add a *_col field for the values
3. Have a dataclass that has a key to indicate a value is a column. E.g. color=ui.TableColumn("X") and then the TableColumn dataclass has metadata indicating it's a column.