Add delete operation to schedules REST resource

Users should be able to delete a job schedule. Currently job schedule resource supports list, detail, cancel operations.

Job schedule resource is a little different than other types of job data such as job executions, job instances, or step executions, in that the job schedule resource does not correspond to any data in job repository.

Need to add delete operation to jberet-rest-api and jberet-vertx/jberet-vertx-rest sub-modules.

Delete operation should do what cancel operation does, and deleting the job schedule record. After a job schedule is successfully deleted, no scheduled job execution under this job schedule will be executed, and there is no record of this job schedule.