Form Element Select: (auto) choose 'mode': 'keys' or 'values'
Fix typo
Form Element 'Radio', 'Checkbox', 'Select': Implement values_mode

Select: rename 'mode' to 'values_mode'
Radio, Checkbox: Use 'values_mode' for these two element types too
Form Element File: Activate; save tmp file in final dir; remember values
Form Element File: Add, but deactivate JavaScript code
Form Element File: Fix JS functions (esp. connect)
Form Element File: show old filename; JS: either show old data or input field
Form Element File: show_element()