Only embed pretix/pretalx scripts on pages using those #39
Description
Right now pretix/pretalx scripts are embedded on every page.
<link rel="stylesheet" type="text/css" href="https://pretix.eu/denog/denog12/widget/v1.css">
<script type="text/javascript" src="https://pretix.eu/widget/v1.en.js" async></script>
<script type="text/javascript" src="https://pretalx.com/denog-meetup-2021-02/schedule/widget/v2.en.js"></script>
<script type="text/javascript" src="https://pretalx.com/denog13/schedule/widget/v2.en.js"></script>
<link rel="stylesheet" type="text/css" href="https://pretix.eu/denog/denog13-workshops/widget/v1.css">
<script type="text/javascript" src="https://pretix.eu/widget/v1.en.js" async></script>