display_html should have a sensible default and support substitutions from cert fields

[stuartf]

It would be nice if when display_html isn't specified it would be populated with something reasonable like:

<img /><!-- the certificate image -->
<h1>{{Certificate Title}}</h1>
<p>Issued on: {{issue date}}</p>
<p>Issuer: {{issuer}}</p>
<p>Recipient: {{recipient}}</p>

Additionally being able to reference fields from the conf or resulting json so that the displayed cert can show recipient info would be nice.

[kimdhamilton]

+1 for this

[ktrev]

Is this feature available now? If yes, how to use it?