Desktop App code editor improvements

The current code editor could be improved. However, this may require to switch to another one (esp, due to no. 1 below), possibly CodeMirror or Monaco, the latter being a bit harder to integrate in Angular, it seems.

What could be improved or is missing:

1. code linting for mix of handlebars and json/xml/etc --> supported by codemirror, but apparently not possible with Ace Editor
2. use vscode keybinding instead of default --> available on both CodeMirror and Ace
3. use Nord theme, to align with website --> available on both CodeMirror and Ace
4. handle font zooming to solve #1659
5. having built-in code formatting would be great

This could solve #884 and maybe #1365