Built-in translation facility

I have implemented a tool to translate the FormSimple interface as well as any action (or tool) that may be present in the source code.

It is integrated into the FormSimple settings page with a single link and a conditional to redirect the request depending on a GET parameter.

It has the ability to create new language files as well as to add and remove strings from language files.

It preserves any comment that may be present in the language files before of the `$FormSimple_lang` declaration.

It also has a built-in rollback facility.

It doesn't interfere with the current translation functions, all other existing functions that retrieve translations strings from the language files are left untouched.

If it makes it into the main repo, I will see how to integrate it with the actual language dropdown within the FormSimple settings page. It will have to be handled as a special case since the FormSimple configuration file isn't treated in a special way and is handled by the same facility that handles any other configuration file.

(For that matter, if it makes it into the main repo, we may see if it's the case to force all actions and tools to comply with this built-in translation framework, by letting it handle any `langs` setting in any configuration file by default regardless of it being the main configuration file or an action's/tool's one)