Change tasks

### Description

Once a task is submitted, there is no way to change it.

### Solution

There should be a seperate window where a task id and password is requested. Once filled in correctly, a form should appear similar to the Add Task form where all the fields are prefilled.

This requires two new elements:
1. Passwords in tasks and an area for the password in the Add Task form;
2. A new view for changing tasks.