Added a feature to execute the next task after the previous one finishes.

This feature enables the user to select a "Consecutive" checkbox for a task, and this would mean that this task will be automatically started after the previous one finishes.

FEATURE: 380445

Reviewers: #kde_applications, kde-utils-devel, aacid

Reviewed By: #kde_applications, aacid

Subscribers: lueck, kde-doc-english, aacid, bcooksley, kde-utils-devel

Tags: #kde_applications

Differential Revision: https://phabricator.kde.org/D10186