Without this Outlook and Windows Mail don't honour the font set at the top level. Note that this change predates all the screenshots I uploaded to the wiki on 2017-02-02, I'd just forgotten to commit them.
Solved the problem of <p> tags being given different padding or color by different clients, without having to copy-paste a string of CSS into every <p> tag in the templates.
Rather than including HTML markup in the locale file (which also has the inconvenience of requiring both a plain-text and an HTML duplicate of the same string), move the markup to the template. Also added a helper to reduce clutter in the template slightly.
