Add styleguide support in the 'undercurrent way'

[mehigh]

I attempted to add styleguide support through the regular gulp-controlled methods, but encountered a couple of issues:
1 - When using it using 'the gulp' way I get an error regarding vinylFs (happenes with the latest Gulp version as well) because vinyl 3 is a breaking update and hence causes a critical error for gulp-util which uses vinyl 2.
2 - when attempting to run the sc5-styleguide-cli from inside our flow, "TypeError: gulp.hasTask is not a function" is an error I constantly got and I think this is causing a conflict between Gulp 4 that we're using and Gulp 3.9.1 the sc5-styleguides is using behind the scenes.
gulp = require('gulp') inside styleguide-cli.js ends up pointing to Gulp 4.0.0 which doesn't have .hasTask defined.

This might be worth picking up when the following issue gets fixed:
SC5/sc5-styleguide#1127

For the moment running using the CLI installed globally is the only way I was able to get it to work to avoid the Gulp versions clash.

Even running npm run styleguide triggers the wrong Gulp version to be loaded inside.