CSS endpoints clarification

[adamkudrna]

Usage of RUI CSS is now confusing.

1. Components CSS used to be part of the JS bundle, but since the docs migration in v0.53, it's no longer there.
2. Styles order in react-ui.css should be changed: components should precede utility classes. May be fixed by CSS cascade layers in Leverage CSS cascade layers to fix and user-proof styles order #518.

[adamkudrna]

Proposed approaches to CSS endpoints:

1. ✅ Provide react-ui[.development].css containing all CSS layers: theme, foundation, components, and helpers. (We have it, just with wrong layers order.) This is the option to get up and running quickly.
2. ⚠️ Let users manually load Sass files with theme, foundation and helpers. Component styles then must be in a standalone Sass file components.scss, or there must be another JS bundle containing also components CSS.
   This scenario is currently broken.