Add Toggle Done functionality to Google Integration

Changes to Google Integration: “Toggle Done” functionality is now
included. Currently, this method can toggle done for Floating and
Deadline tasks on Google Tasks.

Added: toggleDone method in Storage interface instead of vaguely
calling modifyTasks for everything that is supposed to update the task.

Fixes: Re-order IOException and UnknownHostException in affected
classes. UnknownHostException should have be thrown first before
IOException because IOException covers UnknownHostException.

Refactoring: Change “ArrayList” to “List” in two of the methods in
chirptask.storage.Task class.