Move all GTK stuff to a subdirectory.

src/Makefile.am

@@ -14,7 +14,7 @@ test_map_CXXFLAGS = `pkg-config --cflags sdl gl SDL_image`
 test_map_LDADD = libcommon.a
 test_map_LDFLAGS = `pkg-config --libs sdl gl SDL_image`
 
-editor_SOURCES = editor.cpp gtkvideo.cpp
+editor_SOURCES = gtk/editor.cpp gtk/gtkvideo.cpp
 editor_CXXFLAGS = `pkg-config --cflags sdl gl SDL_image gtk+-2.0 gtkgl-2.0`
 editor_LDADD = libcommon.a
 editor_LDFLAGS = `pkg-config --libs sdl gl gtk+-2.0 gtkgl-2.0 SDL_image`