FEATURE #1373: add history of content

This commit contains only core funcionality of displaying history. Module settings must be implemented in each module.

app/Handlers/Contracts/HistoryHandler.php

@@ -0,0 +1,9 @@
+<?php
+namespace App\Handlers\Contracts;
+
+interface HistoryHandler
+{
+    public static function parseColumnName($name);
+
+    public static function parseChangedValue($changeset);
+}