XML+JSON loading and rendering

[renehossle]

1. Implement a progress bar to indicate this could take a while

2. Use Virtual Scroll to decrease render time

Note: Think about how we could avoid big files piling up in the clients cache.

dzu (2023-06-30): Tried Virtual Scrolling. Managed to make it worked as a POC but noticed quite quickly afterwards that the browser's search functionality didn't work as expected as it could only search in the lazy-loaded elements currently visible on the screen. Any other values could not be found even if they were part of the full text.