Fix flickering on some renderers

GLUT apparently doesn't do double buffers by default, (at least
sometimes) so we need to explicitly set it in init.

TODO.md

@@ -11,7 +11,6 @@
 ## Bugs
 - crash when eye goes outside of roi
 - incorrect appdata location on Windows
-- flickering on some renderers
 
 # Whenever
 

src/graphics.cpp

@@ -94,8 +94,9 @@ void initGraphics () {
 	char *argv[1] = {(char*)"fc2d"};
 
 	glutInit(&argc, argv);
-	glutCreateWindow(PROJECT_NAME);
+	glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
 	glutInitWindowSize(512, 512);
+	glutCreateWindow(PROJECT_NAME);
 
 	glewExperimental = GL_TRUE;
 	glewInit();