[MODULES] Introduce the concept of abstract modules to V3

Introduce placeholder for abstract upload and thumb modules
Temporarily supress some bugs

src/Core/Modules/Upload.php

@@ -0,0 +1,11 @@
+<?php
+
+
+namespace App\Core\Modules;
+
+// used by avatar and attachment in note creation; plugins will be able to validate certain filetypes such as images
+
+abstract class Upload
+{
+
+}