Add QR code to PDFs for verification

[alexfigtree]

Is your feature request related to a problem? Please describe.
When a PDF is generated from the wallet there is no way to identify the PDF as being sourced from a Verifiable Credential.

Describe the solution you'd like
The LCW has the ability to generate a link to verifier plus for the credential. We could use this functionality to add a QR code to the PDF that will contain that link. We could consider asking the user if they would like a url added to their PDF.

Describe alternatives you've considered
We could also consider using CBOR (?) to pack the data into the PDF and signing it but that's probably outside the scope of this because a link to verifier plus is far more usable.

Additional context
One of the challenges is that we provide the user with an option to create and destroy a URL. Do we use this url in the PDF and have them create it before exporting or do we keep this functionality separate? Also, links stored in the verifier plus db expire in one year. If we add a url to the PDF, would it be. different one every time the PDF is generated

Implementation details for this ticket

For wallet on share screen:

Check if credential is verified, then
Check if credential has renderMethod field, then
Check if this method has html embedded or a link to an html file
If there is custom html provided by the issuer via a template, in the export to PDF code, look through html for a qr code tag provided by the DCC (let's call it qr_code), so that if we search for {qr_code}, we replace what's in the curly braces with an img element of a QR code of the share link.
Goal is to replace any QR codes provided in a custom html template, NOT to add them.

Follow-up ticket to #604

[alexfigtree]

1. Look for qr_code tag, if exists, then show modal (that looks just like "Share to LinkedIn" modal)
2. "Are you sure" modal - always display if no link