Added a better error message, if no valid language was supplied.

[TwoOfTwelve]

I an invalid language was supplied on the cli the following message is now printed:

Language asdf does not exists. Available languages are: cpp, cpp2, csharp, emf, emf-model, go, java, kotlin, llvmir, python3, rlang, rust, scala, scheme, scxml, swift, text, typescript

[Kr0nox]

With this we could also rethink the available languages message printed at the start

 LanguageLoader - Available languages: '[C/C++ Scanner [basic markup], C/C++ Parser, C# 6 Parser, EMF metamodel, EMF models (dynamically created token set), Go Parser, Javac based AST plugin, Kotlin Parser, LLVMIR Parser, Python3 Parser, R Parser, Rust Language Module, Scala parser, SchemeR4RS Parser [basic markup], SCXML (Statechart XML), Swift Parser, Text Parser (naive), Typescript Parser]'

Since these are the available parsers, not languages as stated in the message. and with #1494 we have two languages that use the same parser and that new language would not be explicitly mentioned in this message

[tsaglam]

@Kr0nox the language loader should check for language interface implementations, and thus the Javascript module should be mentioned when the dependency in the CLI module ist set...