[Android] misc fixes (#4478)

* use product as device model
* print android version (codename + number) + api at launch
* exit the application properly
* fix fullscreen switching (and disable it on newer android versions)
* gettext: lower log level for message: cannot open translation file
* android common settings refactor

frontend/gettext.lua

@@ -51,7 +51,7 @@ function GetText_mt.__index.changeLang(new_lang)
     local po = io.open(file, "r")
 
     if not po then
-        logger.warn("cannot open translation file:", file)
+        logger.dbg("cannot open translation file:", file)
         return false
     end