FormHandler table: test cases for enhancements

Add test cases and documentation for the following features

• Clicking on Add / Edit focuses on the first inpput
• Pressing Enter when editing / adding saves the document
• Custom action receive a .notify(message) that they can use to send a notification
• Custom actions can return a jQuery deferred (e.g. return $.ajax(...)). In that case, it shows a loading indicator, and after the deferred is complete (i.e. .always()), the loading indicator is removed