…version

…` tests (#461)

`happy-dom` is used due to missing HtmlDialogElement support in `jest`.
Just to mention, `happy-dom` provides partial support for dialog element,
so not all test can be implemented.

This commit creates a new folder `src/jsHelpers` for `classNames` and `transferProps`
functions.

The aim is to have the code organization symetric to the
`src/components` folder for better developer orientation.

…n be used

`Modal` can now be colored via the `color` prop, using a value
from the Feedback Colors collection.

We found the Neutral Colors collection insufficiently flexible to use,
so we are removing it from more complex components where its usage
was unclear and confusing.

Features:

- New `--rui-Card__background-color` custom property has been
  introduced to define `Card`'s default background color.

Breaking changes:

- `Alert`: light and dark colors (Neutral Colors collection) have been
  dropped with no replacement.
- `Card`: light color now corresponds to the default appearance.
  The dark color option has been dropped with no replacement.

Migration:

- `Alert`: pick another color from the Feedback Colors collection.
- `Card`: remove `color="light"` to keep the default light appearance.
  If using `color="dark"`, pick another color from the Feedback Colors
  collection.

It ensures that the text is displayed in the font that the user is
most comfortable with, and it also reduces the size of the data
transferred.

Breaking change:

The Titillium web font has been replaced with native font stack.

Migration:

To keep the Titillium web font in your project, load the web font
and override the `--rui-font-family-base` custom property:

```
--rui-font-family-base: 'Titillium Web', helvetica, roboto, arial, sans-serif;
```