Suggestion: Provide basic completion / resolve even if Python SDK with snakecharm not configured

[iromeo]

We could provide basic completion (and hide unresolve ref warning) even if Python SDK with snakecharm not configured.

Not sure that all users will use proper SDK. Probably completion could use some hardcoded list of items, e.g. (config, rules, input, output, log, params, ... + some io.methods) instead of getting all methods from snakemake package.

This is the opposite to Related #109.

P.S: Not sure that we really want to implement this feature. Just a reminder of a possible workaround.