Add setting to enable tracing of language server requests (#28)

* Update vscode dependencies

The vscode package has been deprecated in favor of @types/vscode and
vscode-test.
Details can be found at: https://code.visualstudio.com/updates/v1_36

Also update vscode-languageclient to a newer version to be able to use
new features such as the `traceOutputChannel`.

* Update npm dependencies with security issues

* Add option to trace language server communication

Details: https://code.visualstudio.com/api/language-extensions/language-server-extension-guide#logging-support-for-language-server

This requires changing the name of the LanguageClient to `vhdlls`
because this prefix is used internally to read the settings.

Author: MaximilianKoestler