extracted rebar.config parsing logic to RebarConfigUtil

replaced Processor<> with Consumer<> usages
added include paths parsing from rebar.config for "small IDEs"

added tests for include files resolution
made UnresolvedInclude inspection enabled by default
augmented include path completion for "small IDEs"

added tests for introduced completions
paths from 'include' directories and include paths specified in rebar.config are now suggested when typing in include attributes