make reply-to link depending on screen-width

* on small/smartphone-screens show "reply to" link above the posting and
  an eventual "shared by" link in a second line.
* on middle/tablet-screens show "reply-to" and "shared-by" link in one
  line above the posting, divided by a dot.
* on large screens show reply-to-link next to the time/date-link when
  posting was posted.

the first to positions are better for users with thick fingers on
smartphones. (like me)

Change "in reply to" to "is reply to". Sounds better.

src/Object/Post.php

@@ -502,7 +502,7 @@ class Post
 
 		$tmp_item = [
 			'parentguid'      => $parent_guid,
-			'isreplyto'       => DI::l10n()->t('in reply to %s', $parent_username),
+			'isreplyto'       => DI::l10n()->t('is reply to %s', $parent_username),
 			'template'        => $this->getTemplate(),
 			'type'            => implode('', array_slice(explode('/', $item['verb']), -1)),
 			'comment_firstcollapsed' => false,