Propose guidelines to move to component CSS classes from utility classes

As the "Spring Cleaning" phase of &950 (closed) is in progress, it seems like the first approach we take is utility-only. But it's inevitable to have the need for component classes anyway to:

• account for responsive design
• keep the number of CSS classes in HTML manageable. Example of this going beyond manageable (?) limit https://gitlab.slack.com/archives/C0GQHHPGW/p1555615738062200

This issue aims to discuss when utility-to-component classes should happen.

Possible "signs" of a need for a component class:

• More than one appearance of the same set of utility-classes? For example template + testing fixture
• Too long list of utility classes? What is "too long" then?
• Different presentation on different screen sizes? Do we convert when an element should look differently on at least 2 different resolutions?
• Anything else?

As a follow up of this discussion, documentation should be properly updated.