Webgui-new language service

[barnabasdomozi]

The current implementation of webgui-new only calls the CppService as a Language Service.
This is an issue when requesting information such as getAstNodeInfoByPosition since the CppService gets called even if we are not viewing C++ files.

In this patch, I added a universal language-service for webgui-new, which decides the service to call based on file type.
Before using this language-service, one should call createClient with a file type and then it creates the appropriate Thrift connection.

I also replaced existing CppService calls with the new language-service.

For the codemirror-editor, I also added a languageExtension function, which selects the correct CodeMirror extension for syntax highlight.

[mcserep]

Thanks for refactoring this part. The code looks good, needs functional testing before getting merged.