A few suggestions to improve cake integration

1.  Allowing CakePlugin bootstrap option to load the plugin's bootstrap file to avoid duplicate code through the repeated usage of require_once(). Removed instances where bootstrap was loaded.
2.  Allowing the component to load the helper automatically since both are needed anyway. No need to explicitly load helper once the component is added to controllers.
Added visibility keywords.
3. Updated README.md. Added instruction to use CakePlugin::load('AjaxMultiUpload', array('bootstrap' => true)); so bootstrap is loaded automatically.