Create journal entry when deleting attachments from e-mails

![bildschirmfoto 2014-07-31 um 08 52 07](https://cloud.githubusercontent.com/assets/485600/3760816/3952c98c-187f-11e4-9752-e9f7c226b8d1.png)

There should be an additional entry stating that an attachment was deleted in e-mail xy.
Good point! Added a comment and made the naming more clear in the rest of the code (journal factory, extract_attachments).