added Theme with colors and text

[TouHouNo]

Changes

Adds a new AppThe block that provides all necessary color and text style themes

Checklist

• My code follows the style of this project.
• The code compiles without warnings.
• I have performed a self-review of the changes.
• I have documented my code, in particular the intent of the
  hard-to-understand areas.
• (If necessary) I have updated the CHANGELOG.

CLA acceptance

_Remove if not applicable.

By submitting the contribution I accept the terms and conditions of the
Contributor License Agreement v1.0

• link: https://developers.concordium.com/CLAs/Contributor-License-Agreement-v1.0.pdf

• I accept the above linked CLA.

[rh-concordium]

Hi Szymon,
As agreed in our meeting yesterday, I have copy-pasted your changes (typography, colors, theme) to this PR where we have the whole design system setup, including widgetbook: #33