Add a 'copy to clipboard' button in the API token page

[prioux]

CBRAIN has a page that allows users to generate an API token.

When the token is generated, it is shown int he page and users are expected to write it down/copy it somewhere.

I suggest that just besides the token we had a nice 'copy to clipboard' button.

[MontrealSergiy]

a snippet for that https://www.w3schools.com/howto/howto_js_copy_clipboard.asp

[MontrealSergiy]

also there is a dedicated library, with an old backend https://clipboardjs.com/ with cool button and 'your text is copied' message

https://www.golinuxcloud.com/javascript-copy-to-clipboard/ recommends it as a polyfill/fall-back solution compatible with old browsers.