[ATTACHMENTS] Even more further refactoring

Introduce Encoder plugins Instead of abstract upload and thumb modules

Ported attachment routes. In v3 thumbnail depends on existing attachment
so route updated accordingly.

src/Core/Modules/AttachmentThumbnail.php

@@ -1,9 +0,0 @@
-<?php
-
-namespace App\Core\Modules;
-
-// an interface that specifies how thumbs shall be created, allowing for generation of image, video, pdf, wtv by plugin
-
-abstract class AttachmentThumbnail
-{
-}

src/Core/Modules/AttachmentValidate.php

@@ -1,10 +0,0 @@
-<?php
-
-namespace App\Core\Modules;
-
-// Remote Download allow to create a file or to download directly as a thumbnail; same plugins as for upload will validate
-// as validation event will be the same as that of upload - same logic
-
-abstract class AttachmentValidate
-{
-}