about: use activitypub for contact and homepage for derf link

<div class="row">

	<div class="col s12">

		<a href="https://finalrewind.org/projects/travelynx">travelynx</a> v<%= stash('version') // '???' %><br/>

		Entwickelt von <a href="https://social.skyshaper.org/derf">derf</a><br/>

		Entwickelt von <a href="https://finalrewind.org">derf</a><br/>

		<a href="<%= app->config->{ref}{source} // 'https://github.com/derf/travelynx' %>">Quelltext</a> lizensiert unter AGPL v3<br/><br/>

		Backends:

		<a href="https://finalrewind.org/projects/Travel-Status-DE-IRIS/">Travel::Status::DE::IRIS</a>

<div class="row">

	<div class="col s12 m12 l4 center-align" style="margin-top: 1em;">

		<a href="https://finalrewind.org/me/" class="waves-effect waves-light btn"><i class="material-icons left">message</i>Kontakt</a>

		<a href="https://social.skyshaper.org/derf" class="waves-effect waves-light btn"><i class="material-icons left">message</i>Kontakt</a>

	</div>

	<div class="col s12 m12 l4 center-align" style="margin-top: 1em;">

		% if (my $issue_url = app->config->{ref}{issues}) {