More Spin locks experiments

[vsonnier]

Contrary to what I said in #713, ThreadBlockingQueue can support SpinMutex through the usage of std::condition_variable_any. Turns out the "sleep or wake" semantic is done through the condition variable not the lock itself.
Lets try this.
Also reverted spin-lock usage in WaterfallCanvas, the operation is not that short-lived, so a proper std::mutex is more fitted there.