languages menu moved to xml + minor refactor

res/layouts/pages/languages.xml

@@ -0,0 +1,3 @@
+<panel size='400' color='#00000080' padding='8'>
+    <!-- content is generated in script -->
+</panel>

res/layouts/pages/languages.xml.lua

@@ -0,0 +1,19 @@
+function on_open()
+    local locales = gui.get_locales_info()
+    local invlocales = {}
+    local names = {}
+    for k, v in pairs(locales) do
+        table.insert(names, v.name)
+        invlocales[v.name] = k
+    end
+    table.sort(names)
+    
+    local panel = document.root
+    for _,k in ipairs(names) do
+        panel:add(string.format(
+            "<button onclick=%q padding='10'>%s</button>",
+            string.format("gui.set_locale(%q) menu:back()", invlocales[k]), k
+        ))
+    end
+    panel:add("<button padding='10' onclick='menu:back()'>@Back</button>")
+end