Title: Regression: Ability to assign sortable hidden properties to table cells (as found in previous versions)

Description: In earlier versions of MDB, it was possible to associate a hidden property with a cell that could be used for sorting. For example, in a column of text-formatted dates, the cell could have a hidden property that was the Unix timestamp of the date. Users were able to indicate that the column should be sorted using this hidden property. This feature now appears to be absent or non-functional in the most recent version.

Expected behavior: Users should be able to assign a property to a given cell (hidden or otherwise), which could later be used for sorting. In a column of text-formatted dates, a cell could contain a hidden property — for example, the Unix timestamp of that date. It should be possible to indicate that this column uses the hidden property for sorting.

Actual behavior This feature does not seem to exist in the current version, or if it does, it is nonfunctional. Attempting to sort a table column based on the hidden properties of its cells does not result in the expected sorted order.

Resources (screenshots, code snippets etc.) This is an example of how the feature used to function:

<td class="align-middle" data-sort="{{ row.timestamp }}">
                    {{ row.localized_time }}
 </td>