Support importing cover images via the new infrastructure

Author: thekid

src/main/php/de/thekid/dialog/import/Cover.php

@@ -0,0 +1,24 @@
+<?php namespace de\thekid\dialog\import;
+
+use de\thekid\dialog\processing\Files;
+
+/** Imports the cover image */ 
+class Content extends Source {
+
+  public function entryFrom(Description $description): array<string, mixed> {
+    return [
+      'slug'      => '@cover',
+      'parent'    => '~',
+      'date'      => $description->meta['date'],
+      'title'     => $description->meta['title'],
+      'keywords'  => $description->meta['keywords'] ?? [],
+      'content'   => $description->content,
+      'locations' => [...$description->locations($description->meta['date']->getTimeZone())],
+      'is'        => ['cover' => true],
+    ];
+  }
+
+  public function contentsIn(Files $files): iterable {
+    yield from $this->mediaIn($files);
+  }
+}