Fix copy button on HTTP sites

[jennydaman]

In #782 a feature was added which depends on the navigator API. However, this API is only available on "secure" sites: either when the site is on localhost or when HTTPS is being used.

The bug can be reproduced by running ChRIS_ui locally but accessing it from a non-localhost URL, e.g. using your computer's hostname instead. You'll get the error

Uncaught TypeError: navigator.clipboard is undefined

A workaround is described here: https://stackoverflow.com/a/65996386