Implement rollback ability for DCM Logical Clouds

With the introduction of updatable Logical Clouds in %22.03 via #120 (closed), another desired feature is to be able to rollback an updated logical cloud to its previous version. This should be achieved with the introduction of a new /rollback API method that resurrects the previous version of a Logical Cloud according to the previous appcontext (which remains saved until the logical cloud is deleted).