Review all threading code and use Xdispatch where possible

[Roflincopter]

Some threading issues require sequential execution. These can be enforced by for instance condition variables. Unfortunately there are currently some issues with condition variables in libc++ so to avoid these issues we are going to use xdispatch. But first we need to identify the pieces of code we want to rewrite using xdispatch and how we should do that.

blocks on #1

[Roflincopter]

Although xdispatch looked promising the lack of direct dependency support with tasks is too great of a lack in my regard, And with std::thread being available and as it seems fully functional in the windows build not needed anymore.