Consider using manager_poll in executor/task wait function

[shuds13]

This could be added to the wait function to kill a running application on receiving a kill signal (similar to the polling_loop function). Probably using an optional argument.

One issue to consider here that wait works on a task, and so automatically kills the current task. How would this work in a multiple task scenario. The use of push back in manager_poll may already enable this to work if applied to multiple tasks.

As manager_poll is an executor function, it may be that this would need to be an executor rather than a task function - similar to polling_loop.

In that case, ability to add a list of tasks could also be considered.