UI: add tool panel for node editor, use tabs

This follows the 3D view, adding an "Options" tab.

source/blender/editors/space_node/space_node.c

@@ -1001,6 +1001,7 @@ void ED_spacetype_node(void)
   art->prefsizex = UI_SIDEBAR_PANEL_WIDTH;
   art->keymapflag = ED_KEYMAP_UI | ED_KEYMAP_FRAMES;
   art->listener = node_region_listener;
+  art->message_subscribe = ED_area_do_mgs_subscribe_for_tool_ui;
   art->init = node_buttons_region_init;
   art->draw = node_buttons_region_draw;
   BLI_addhead(&st->regiontypes, art);