Use JsTrans as a component. Load messages from ANY CMessageSource instance

- Use JsTrans as a component and configure it in config/main.php :
'preload'=>array('jsTrans', ... ),
...
'components'=>array(
  'jsTrans'=>array(
    'class'=>'ext.JsTrans.JsTrans',
    'categories'=>array('app'),
    'languages'=>array('fr','es')
  ),
  ...
- Load messages from ANY CMessageSource instance, using Reflection to call protected
method loadMessages() from Yii::app()->messages component
enclose eval in try/catch block

bug correction for translating 'Invoice #{0}', 
which was causing an exception
adding onMissingTranslation for handling untranslated messages

enabling this option will trigger an ajax GET call to the specified
route, allowing to trigger an onMissingTranslation event server-side
readme wasn't properly formatted
corrected bug when translation is null
Merge pull request #11 from cnlevy/patch-2

Use JsTrans as a component. Load messages from ANY CMessageSource instance