[TASK] Clean up class alias mechanism

* adopt class loader to load the class alias map from a location
  Migrations/Code/ClassAliasMap.php in every extensions path
* split up core class alias map into extension class alias maps
* adopt tests to the compound class loader cache

Change-Id: I7102fd5aab7a6364d5bcb5603f011dfcdb859ec9
Resolves: #41012
Resolves: #41013
Related: #40095
Releases: 6.0
Reviewed-on: http://review.typo3.org/15085
Reviewed-by: Thomas Maroschik
Tested-by: Thomas Maroschik
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel

Migrations/Code/ClassAliasMap.php

@@ -0,0 +1,5 @@
+<?php
+return array(
+	'tx_feedit_editpanel' => 'TYPO3\\CMS\\Feedit\\FrontendEditPanel',
+);
+?>