Version the .curry/language-server folder

[fwcd]

We'd want to make sure that different versions of the language server can coexist, even if we make breaking changes to the ICurry format (e.g. as proposed in #26 (comment)).

Therefore we should include the language server version in the output directory path (e.g. .curry/language-server-x.y.z) and make sure this version number is bumped (at least) every time there is a breaking change in one of the serialized formats.