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/engine/configurationmanager.cpp

@@ -57,6 +57,7 @@ const string ConfigurationManager::KeyKeyboardShortcuts = "KeyboardShortcuts";
 const string ConfigurationManager::KeyDocumentation = "Documentation";
 const string ConfigurationManager::KeyFactoryDocumentation = "FactoryDocumentation";
 const string ConfigurationManager::KeyConfigScene = "Scene";
+const string ConfigurationManager::KeyConfigTask = "Task";
 
 const string ConfigurationManager::KeyLogging = "Logging";
 const string ConfigurationManager::PartLogLevel = "LogLevel";