Text in donate.tpo has too much HTML to be localizable

The text in the donate page has a lot of HTML that makes it very hard to translate correctly, for example the <p> and <strong> tags at https://gitweb.torproject.org/project/web/donate-static.git/tree/content/privacy-policy/contents.lr

We should use markdown for the content, and style with templates and CSS. As the other lektors do.

This needs to happen before we send the strings for localization.