First own language server approach

[katauber]

After the from Xtext generated lanuaguage server for Metafacture Fix and Flux is very simple, we want a language server which supports some more features. So we need to implement our own language server.
There language server protocol bases like lsp4clj or lsp4j which I think we should use. I prefer clojure as always :)

First we thought a good start could be to reimplement the function of the existing Fix language server.
We first need the parser of our language, so the first step could be moving from Xtext to ANTLR for Metafacture Fix.
@fsteeg and I discussed offline that we also could start with a language server for Metafactre Flux, because Metafacture Flux in Metafacture Core already uses ANTLR.
So the first step is to implement a minimal language server for Metafacture Flux with lsp4clj or lsp4j