Handle CORS errors nicely when loading a custom version of EDAM

[hmenager]

Current behaviour

Whenever a user loads a custom version of EDAM, if there is an error while loading the URL the UI will give no error message and no feedback:

Suggested improvements

• Display an error message when an error occurs while loading the file, then go back to the previous version selected.
• If possible, the error message should be specific and readable, e.g. explain if this is a CORS error, or if the file doesn't seem to be in the right format.

[HagerDakroury]

thamks @hmenager. A super important issue here.
Also, mind passing the link you were trying to load?

[hmenager]

Sure, it happened to me while trying to test how MONDO would display, with this file:
https://github.com/monarch-initiative/mondo/releases/download/v2021-07-12/mondo-minimal.owl
But you can also test it with EDAM URLs which are not from raw.githubusercontent.com, such as:
https://github.com/edamontology/edamontology/releases/download/1.25/EDAM_1.25.owl
(that's important, because users might want to paste such "release" URLs directly)

[matuskalas]

Is this the CORS error?