Remove theme-options.yml feature

Problem/Motivation

Remove theme-options.yml feature. We never really use this yaml file to build some additional features around it, it is confusing, adding additional layer of complexity and IDE can not autocomplete variables that are defined there.

Projects that want's to continue using theme-options.yml can move this code to it's base theme and also consider to replace gulp-sass-inject node lib with https://www.npmjs.com/package/gulp-sass-vars.

If not too complicated to implement use update theme function or some script to transform yaml to sass?