Remove routing from application

[oxcabe]

Description

Routes have been object of state related issues in the past (e.g. see: #48).

Proposed solution

This issue proposes removing the unnecessary complexity routing provides in its entirety. This is in line with refactoring the UI into a more godbolt-like (see: godbolt.org/) experience.

Tasks

1. Remove react-router from the project.
2. Create a generic simulator layout UI as the new "landing page".
3. Adapt the simulator specific widgets to connect to this layout.
4. Add a simulator selector into the toolbar. Use double confirmation (alert dialog?) to avoid accidental state reset by users.
5. Design a new "Welcome" window that will be shown before a simulator is selected.