support SVG logo in dokuwiki template

Inspired by https://forum.dokuwiki.org/d/20964-logo-too-big this adds
SVG support for setting the logo in the dokuwiki template.

Note: This introduces a fixed height for the logo (64px), previously
users could decide their logo size by simply uploading it in the right
size. Users who want a larger sized logo will have to override the
height in a userstyle now

lib/tpl/dokuwiki/css/design.less

@@ -35,6 +35,7 @@
         img {
             float: left;
             margin-right: .5em;
+            height: 64px;
         }
 
         span {

lib/tpl/dokuwiki/tpl_header.php

@@ -19,13 +19,18 @@
 
         <h1 class="logo"><?php
             // get logo either out of the template images folder or data/media folder
-            $logoSize = array();
-            $logo = tpl_getMediaFile(array(':wiki:logo.png', ':logo.png', 'images/logo.png'), false, $logoSize);
+            $logoSize = [];
+            $logo = tpl_getMediaFile([
+                ':wiki:logo.svg', ':logo.svg',
+                ':wiki:logo.png', ':logo.png',
+                'images/logo.svg', 'images/logo.png'
+            ], false, $logoSize);
 
             // display logo and wiki title in a link to the home page
             tpl_link(
                 wl(),
-                '<img src="'.$logo.'" '.$logoSize[3].' alt="" /> <span>'.$conf['title'].'</span>',
+                '<img src="' . $logo . '" ' . ($logoSize ? $logoSize[3] : '') . ' alt="" />' .
+                '<span>' . $conf['title'] . '</span>',
                 'accesskey="h" title="' . tpl_getLang('home') . ' [h]"'
             );
         ?></h1>