[Media] Fix issues with database file storage

Fixed file quota as well.

There can be more than one file for the same filehash IF the url are different.

Possible states:
  - A file with no url and with filename is a local file.
  - A file with an url but no filename is a remote file that wasn't fetched,
    not even the thumbnail.
  - A file with an url and filename is a fetched remote file (maybe just a
    thumbnail of it).
  - A file with no filename nor url is a redirect.

Routes:
  Given these states, updated routes so that an attachment can only be
  retrieved by id and a file by filehash.

Major API changes:
  File::getByHash now returns a yield of files

Major UI changes:
  - Now remote non stored files are presented.
  - /view became preferred
  - Redirects to remote originals are preferred.

Many other minor bug fixes...

plugins/Embed/actions/oembed.php

@@ -93,7 +93,7 @@ class OEmbedAction extends Action
                 }
                 try {
                     $thumb = $attachment->getThumbnail();
-                    $thumb_url = File_thumbnail::url($thumb->filename);
+                    $thumb_url = $thumb->getUrl();
                     $oembed['thumbnail_url'] = $thumb_url;
                     break;  // only first one
                 } catch (UseFileAsThumbnailException $e) {