Settings: Proper priority hierarchy

Remove old defaults system
Introduce priority-based fallback list
Use new functions for map_meta special functions
Change groups to use end tags

Unittest changes:
 * Adapt unittest to the new code
 * Compare Settings objects

src/script/lua_api/l_mapgen.cpp

@@ -982,7 +982,7 @@ int ModApiMapgen::l_set_noiseparams(lua_State *L)
 
 	bool set_default = !lua_isboolean(L, 3) || readParam<bool>(L, 3);
 
-	g_settings->setNoiseParams(name, np, set_default);
+	Settings::getLayer(set_default ? SL_DEFAULTS : SL_GLOBAL)->setNoiseParams(name, np);
 
 	return 0;
 }

src/script/lua_api/l_settings.cpp

@@ -197,7 +197,7 @@ int LuaSettings::l_set_np_group(lua_State *L)
 
 	SET_SECURITY_CHECK(L, key);
 
-	o->m_settings->setNoiseParams(key, value, false);
+	o->m_settings->setNoiseParams(key, value);
 
 	return 0;
 }

src/script/scripting_mainmenu.cpp

@@ -31,7 +31,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 extern "C" {
 #include "lualib.h"
 }
-
+#include "settings.h"
 #define MAINMENU_NUM_ASYNC_THREADS 4