Add support for converting and rendering volumetric data in the cdf format. Replace DataConverter by a more general purpose TaskRunner.

Conflicts:
	modules/volume/CMakeLists.txt
	modules/volume/linearlrucache.h
	src/engine/openspaceengine.cpp

src/util/progressbar.cpp

@@ -42,7 +42,7 @@ ProgressBar::~ProgressBar() {
 }
 
 void ProgressBar::print(int current) {
-    float progress = static_cast<float>(current) / static_cast<float>(_end - 1);
+    float progress = static_cast<float>(current) / static_cast<float>(_end);
     int iprogress = static_cast<int>(progress*100.0f);
     if (iprogress != _previous) {
         int pos = static_cast<int>(static_cast<float>(_width)* progress);