Added AbstractPluginUpdater to easily perform updates. 

Usage: 
$updater = new My\Updater(5); //update to Revision 5
$updater->run();

git-svn-id: http://www.pimcore.org/svn/pimcore/private/core/trunk@5505 1f8fe7d8-47f0-464c-8d0a-336f4953ab05