added file modifyTasks.gs         to cope with modifying the array of tasks.
it has two functions: modifyTasks() the prime function and editTasksArray() which is called by modifyTasks.

This separates functions that modify and return a task arrays - file: modifyTasks.gs
and functions that update each task in an array - file: updateTasks.gs

Tested editTasksArray for one case Delete.
WIP: editTasksAry()  coding for Clone

The code seems to work but one of the tests isn't finding two instances
of the task.