[IMP] project: improve project form view usability

Some points have to be improved

 * 'Name of the tasks' field should always be visible. It shows the user such
   a change in configuration is possible;
 * tasks stat button is a way for the user to create a new task from the
   project form view. Just like the subtasks stat button that always shows
   on the task formview;
 * as he might be changing the 'name of the tasks', he should see the
   consequence of this change in the stat button (as the 'name of tasks'
   field might not directly speak to everyone, it is a way to show them what
   this field does);

This commit is linked to task ID 1884015 and closes PR #26906 .