Fix AceEditor errors, or replace it with plain textbox

[dmitrizagidulin]

To reproduce: Go to https://digitalcredentials.github.io/sandbox/ and enable browser console (e.g. Ctrl-Shift-i on linux).
Click on 'Sign Credential' button. Notice in the Console two errors:
Error one:

Unable to infer path to ace from script src, use ace.config.set('basePath', 'path') 
to enable dynamic loading of modes and themes or with webpack use ace/webpack-resolver

(this is likely similar issue to securingsincity/react-ace#766 )

Error two:

GET https://digitalcredentials.github.io/sandbox/mode-mode.js net::ERR_ABORTED 404

Note that on localhost, this error changes to:

Uncaught SyntaxError: Unexpected token '<' (at mode-mode.js:1:1)

Please fix these, as they are preventing console.log from running in signCredential() (for example, try putting a console.log('ISSUING') as the first line of signCredential() in local.ts. Notice that it does not fire, although the credential json is returned.).

Also, fix the Worker error (for example, by adding the following to the AceEditor component):

        setOptions={{
          useWorker: false
        }}

If no solution is found, please remove AceEditor, we can just use a plain textbox for the input.

[fields37]

Hopefully resolved in #80