Add option to force schedule to allocate all its task to the resource of a pool

[JuliaReich]

We love the idea of resource pools, however we have schedules in place which consist of multiple tasks. We would like to use these schedules with a resoure pool so that the first available resource will start working on the schedule, but with the option to force the schedule to allocate all its following tasks to the same resource that started working on its first task. This way we would be able to make sure that all tasks of a schedule are handled by only one resource.