Add 'dev mode' to the language service

This PR adds a a few points that can be consumed by consumes of language service. These points are not hooked up to the VS part yet, current assumption about their behavior is following:
- trace - writes a string to debug output
- error - brings a popup with a  given text

also I've added an extra method `getApiVersion` that can be used to check the version of API and thus to validate assumptions about the its shape