Clean up gulp or perhaps consider better options (hint: parcel!)

[kgrz]

I tried running the CSS compiler and ran into some inconveniences:

• The browersync watcher starts up for every single invocation. Ideally it should only do that when the user runs watch or related commands

• Move away from Gulp ruby and use node-sass. The latter is much better supported in the Node ecosystem and avoid the jump between ruby and node.

• It's worthwhile to consider using a new configless bundler like parcel. I personally found it very simple to use. We can get rid of most of the gulp dependency and package.json also!