Add and remove tasks

[ShingiraiBhengesa]

In this branch, I made the following changes.

• Removed all hardcoded items from the tasks array.
• Created a new JavaScript file for the new functionality.
• implement a function for adding a new task.
• implement a function for deleting a task.
• implement a function for editing task descriptions.
• By default new tasks have the property completed set to false and the property index set to the value of the new array length.
• Deleting a task should update all remaining items' indexes, so they represent the current list order and are unique.
• All changes to the To-Do List are saved in local storage.