Check if webcrypto is available at all

[Lex-2008]

We should detect availability of webcrypto and show a nice message if it's not available. And not allow user to do anything else.

[rileythomp]

Does this just need a check for (window.crypto.subtle != null && window.crypto.subtle != undefined) ?

[Lex-2008]

Yes. Javascript-wise I would do just if(!window.crypto.subtle) for simplicity, and if it's the case - disable all controls on the page and show an error message in the error message box.