Allow unique input to the GUI

Move GUI from RenderEngine to OpenSpace engine

include/openspace/engine/gui.h

@@ -38,7 +38,12 @@ public:
 	void initializeGL();
 	void deinitializeGL();
 
-	void render(float deltaTime, const glm::vec2& mousePos, bool mouseButtonsPressed[2]);
+	bool mouseButtonCallback(int key, int action);
+	bool keyCallback(int key, int action);
+	bool charCallback(unsigned int character);
+
+	void startFrame(float deltaTime, const glm::vec2& mousePos, bool mouseButtonsPressed[2]);
+	void endFrame();
 };
 
 } // namespace openspace

include/openspace/engine/openspaceengine.h

@@ -34,7 +34,7 @@
 
 namespace openspace {
 
-// Forward declare to minimize dependencies
+class GUI;
 class SyncBuffer;
 class LuaConsole;
 
@@ -95,6 +95,7 @@ private:
 	scripting::ScriptEngine _scriptEngine;
 	ghoul::cmdparser::CommandlineParser _commandlineParser;
 	LuaConsole _console;
+	GUI* _gui;
 
 	SyncBuffer* _syncBuffer;