lua add submenu module + cleanup

allows menus + submenus + context menus all with simple tables
menu_t which is a table of strings
func_t which are the corresponding functions to go with those strings

see lua_scripts/submenu_demo.lua

Change-Id: I907b74b4abef0ecbe49f181d0ced6e6d20e94de5

apps/plugins/lua/include_lua/menucoresettings.lua

@@ -0,0 +1,46 @@
+--menu core settings loaded from rockbox user settings
+--Bilgus 4/2021
+
+local function get_core_settings()
+    local rbs_is_loaded = (package.loaded.rbsettings ~= nil)
+    local s_is_loaded = (package.loaded.settings ~= nil)
+
+    require("rbsettings")
+    require("settings")
+    rb.metadata = nil -- remove track metadata settings
+
+    local rb_settings = rb.settings.dump('global_settings', "system")
+    local color_table = {}
+    local talk_table = {}
+    local list_settings_table = {}
+    local list_settings = "cursor_style|show_icons|statusbar|scrollbar|scrollbar_width|list_separator_height|backdrop_file|"
+    for key, value in pairs(rb_settings) do
+            key = key or ""
+            if (key:find("color")) then
+                    color_table[key]=value
+            elseif (key:find("talk")) then
+                    talk_table[key]=value
+            elseif (list_settings:find(key)) then
+                    list_settings_table[key]=value
+            end
+    end
+
+    if not s_is_loaded then
+        rb.settings = nil
+        package.loaded.settings = nil
+    end
+
+    if not rbs_is_loaded then
+        rb.system = nil
+        rb.metadata = nil
+        package.loaded.rbsettings = nil
+    end
+
+    rb.core_color_table = color_table
+    rb.core_talk_table = talk_table
+    rb.core_list_settings_table = list_settings_table
+end
+get_core_settings()
+get_core_settings = nil
+package.loaded.menucoresettings = nil
+collectgarbage("collect")