Task: Move web app code to a separate repository

[apdavison]

To improve maintainability and reporting, we have decided to move code related to the web apps to a separate Github project, retaining the web service (REST API) code in this repository.

Steps:

• [x] copy app code to https://github.com/HumanBrainProject/model-catalog, filtering commits to retain the relevant history
• [x] update CI config to use the new repository
• [x] move tickets with the label "WebApps v2" to the new repository
• [x] remove app code from this repository (we will retain the git history relating to apps, however)
• [x] ensure all documentation is updated accordingly