Suggestion: priorities in IdleQueue

[dagoltz]

It would be nice to be able to add prioritized tasks to an IdleQueue.
We currently have a use case to preload components and would like to preload them by priority - not by order of insertion.
This could either be included in IdleQueue (with the default behavior of a regular queue when no priorities provided) or in a new class: IdlePriorityQueue.

I am willing to create a PR.