Allow custom classes on FormHandler table

Adding styles to FormHandler template components (table, count, page, size, export, filters, search, dropdown, ...) would be easier if we had a class element that we could add to each.

For example,

• columns[..].classes: add the classes to the specified column's <td>
• tableClasses: adds the classes mentioned to each table. Defaults to "table table-sm table-striped"
• rowClass: adds the classes to each row. Defaults to ""