Restructuring for OpenSpace tests

- Moved all OpenSpace headers to separate include directory
- Added OpenSpaceTests binary with OPENSPACE_HAVE_TESTS define
- Added CMake setting of BASE_DIR
- Added OpenSpace initial tests for SceneGraph and SceneGraphNodes
- Added OpenSpace initial tests for psc and pss
- Restructured OpenSpace so no GL functions are called in constructors
to make the classes testable

- Todo: Make the base dir possible to set through command line argument
and configuration file

include/openspace/rendering/renderable.h

@@ -0,0 +1,36 @@
+#ifndef RENDERABLE_H
+#define RENDERABLE_H
+
+// open space includes
+#include <openspace/util/psc.h>
+#include <openspace/util/pss.h>
+#include <openspace/util/camera.h>
+#include <ghoul/misc/dictionary.h>
+
+namespace openspace {
+
+class Renderable {
+public:
+    
+	// constructors & destructor
+	Renderable(const ghoul::Dictionary& dictionary);
+    virtual ~Renderable();
+	
+    virtual bool initialize() = 0;
+    virtual bool deinitialize() = 0;
+    
+	void setBoundingSphere(const pss &boundingSphere);
+	const pss &getBoundingSphere();
+
+	virtual void render(const Camera *camera, const psc &thisPosition) = 0;
+	virtual void update();
+protected:
+	Renderable();
+private:
+	pss boundingSphere_;
+
+};
+
+} // namespace openspace
+
+#endif