when you put sharepoint object under iframe(by creating a widget), you will lose capabilities to edit.
The only way is to create a visualization extension , that will read data from object(like list, csv etc) and show it in your custom html display. Give a form to user to add new row and on click of a button write it back to sharepoint.
Both read and write will have to be done using ajax call(in javascript events) to REST API for read and write of sharepoint.
