Exposed ability to set the tolerance before the pool will begin erasing items.
Modified the way in which pooled items are tracked to remove a number of O(n) searches.
Modified the check for duplicate items into an assert so its caught in debug but not in release.
Merge remote-tracking branch 'remotes/alexparlett/feature/pooled-work-queue'
Acquire event data for work item completion only when necessary. These are pooled by the Context so it shouldn't hurt performance.
Added a square Urho icon (same as the Android icon) to use for the samples on desktop.
Merge remote-tracking branch 'upstream/master'

Conflicts:
	Bin/Data/LuaScripts/Utilities/Sample.lua
	Source/Engine/Core/WorkQueue.cpp
	Source/Samples/Sample.inl