Added WorkManager to manage background tasks.

Relies heavily on the QThreadPool.

core/WorkManager.cpp

@@ -0,0 +1,47 @@
+#include "WorkManager.h"
+
+#include <QRunnable.h>
+#include <QThreadPool.h>
+#include <deque>
+#include <functional>
+#include <mutex>
+
+
+class WorkManagerImpl: public WorkManager {
+public:
+	virtual void addRunnable(QRunnable *runnable) override;
+	virtual void addWork(Work work) override;
+};
+
+
+
+std::shared_ptr<WorkManager> WorkManager::getWorkManager()
+{
+	static std::shared_ptr<WorkManager> wm = std::make_shared<WorkManagerImpl>();
+	return wm;
+}
+
+void WorkManagerImpl::addRunnable(QRunnable *runnable)
+{
+	auto tp = QThreadPool::globalInstance();
+	tp->start(runnable);
+}
+
+class CallableTask : public QRunnable {
+public:
+	CallableTask(WorkManager::Work &&w)
+		: work(std::move(w))
+	{}
+protected:
+	void run()
+	{
+		work();
+	}
+private:
+	WorkManager::Work work;
+};
+
+void WorkManagerImpl::addWork(Work work)
+{
+	addRunnable(new CallableTask(std::move(work)));
+}