ENGINES: Add a new 'renderer' option to replace 'soft_renderer'

'soft_renderer' was a bool and was not useful to select a renderer
in a list with more than two values.

engines/grim/gfx_opengl_shaders.cpp

@@ -205,7 +205,7 @@ Math::Matrix4 makeFrustumMatrix(double left, double right, double bottom, double
 	return proj;
 }
 
-GfxBase *CreateGfxOpenGL() {
+GfxBase *CreateGfxOpenGLShader() {
 	return new GfxOpenGLS();
 }