Codechange: Move dropdown and slider out of widgets directory. (#12403)

Also shuffle headers to place widget includes near end.

This leaves the widgets directory solely for defining Widget IDs.

src/league_gui.cpp

@@ -9,7 +9,6 @@
 
 #include "stdafx.h"
 #include "league_gui.h"
-
 #include "company_base.h"
 #include "company_gui.h"
 #include "gui.h"
@@ -22,7 +21,9 @@
 #include "town.h"
 #include "viewport_func.h"
 #include "window_gui.h"
+
 #include "widgets/league_widget.h"
+
 #include "table/strings.h"
 #include "table/sprites.h"