Loading text / icon does not load

[danieldegroot2]

'loading...' text and/or spinner icon (rotating partial circle) to indicate page is (still) loading does not load.

Example https://knooppuntnet.nl/nl/analysis/changes takes a moment to load (at least currently)

(if not yet added); if page fails with error (and is no longer loading), display error message instead, i.e. when query wizard / API / diffs are down. though I have not experienced such error with Knooppuntnet yet. (feel free to split it into a separate issue)