New plugin event 'OnMODXInit'

This event fired in $modx->initialize().
All request hit this event.

For example, the MODX Manager with Multi language runs on Opera browser in following codes. 

check event:OnMODXInit

```php
if( $modx->event->name == 'OnMODXInit'
  && stripos($_SERVER['HTTP_USER_AGENT'],'Opera') !== false
  && stripos($_SERVER['CONTENT_TYPE'],'x-www-form-urlencoded') !== false
  && strcasecmp($_SERVER['HTTP_CONTENT_TRANSFER_ENCODING'],'binary') == 0 ){
    foreach($_POST as $key => $val){
      $_POST[$key] = urldecode($val);
      $_REQUEST[$key] = $_POST[$key];
    }
}
```