Purpose

To update the Concordium logo on the dev doc site in accordance with the rebranding.

Changes

Updated the following files in Source/Static:

• concordium-logo-dark.svg
• concordium-logo.svg

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.
  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