Be more graceful with faulty HTML (created from famous email clients) which are interpreted by all browsers gracefully, too

[carli2]

A famous email client creates quotations with <blockquote style="width: 100%%">. This is faulty CSS however all browsers I tested interpreted %% as % but not as px. Mpdf however defaults to "px" interpretation which leads to 100px wide blockquotes which in consequence creates PDF documents with a very small stripe of text, lots of line breaks and a large number of pages.

So we should mimic the browser's behaviour and interpret CSS measurements with %% as unit as percent rather than pixels.