Inherit Queue for completion check

Addresses concerns over completion checks and cleanup tasks occurring in the default queue in BigSky. 

Three configurable options were added

cleanupqueue - where cleanup tasks for completion markers should be run
cleanupdelay - how long should cleanup tasks be delayed
defaultqueue - what is the default queue for completion and cleanup tasks (if no cleanupqueue is defined)

Completion checks will now inherit which queue they will run in from the tasks that kick them off. There is a new example of how this works added to the examples folder called context_inherit.

This pattern of inheritance allows greater freedom to shard async's across different queues and balance out their own performance (completion performance included). 

@beaulyddon-wf @tylertreat @tannermiller-wf @johnlockwood-wf