HTML in Sparkle popup should be rendered

[mbacchi]

Description

In issue #9274 (comment) we changed the URL of the changelog, but while testing it to see if I could make it a hyperlink, I found nothing I tried would allow HTML to be rendered properly.

I don't know if this is due to omaha-server storing the release_notes as a Django models.TextField, or if the Sparkle version we're using is not working properly and failing to render the HTML.

This is what the popup looks like currently:

[mbacchi]

Talked to @mherrmann and he suggested this: omaha-consulting/omaha-server#364