Localize HeliosLauncher UI using lang files

[Kamesuta]

This pull request adds the following features:

• Externalize the UI text into lang files and replace them with embedded codes using LangLoader.
  • In ejs files, use the ejs output tag (<%- lang('～') %>) syntax.
• Support argument expansion in LangLoader. Expand the object in the second argument from {placeHolder}.
• Replace json with toml for easier element addition and indentation.
  • If you don't like toml, you can revert the last commit to go back to json.

[dscalzi]

I will take a look, this would be a very nice addition

[luisBazanDev]

It is a very good implementation, I hope you can accept it as soon as possible so I can do the translation into Spanish.

[Codixer]

I wonder the state of this 0_0

[Kamesuta]

Updated: Added cascadable language system for easy customization by launcher forkers.

• Translators can now change the language by simply adding a file like ja_JP.toml and uncommenting //exports.loadLanguage('xx_XX') in langloader.js.
  • You can add only the text you wish to translate to the language file you have added. For items that are not written, the default en_US text will be used
  • This change is ready to accept Pull Requests to add toml files for various languages
• I have separated the following two files that have nothing to do with translation into separate files
  • _placeholder.toml for texts that do not require translation (such as placeholder news article, and default overlay description)
  • _custom.toml for launcher customizer (such as app title, github url, and welcome description)

[dscalzi]

Sorry this has taken a while, mostly looks good - I just need to checkout the branch and test a few things.

[dscalzi]

LGTM, may tweak more later.