Extract attachments: Improve consistency in wording

![bildschirmfoto 2014-07-31 um 08 41 46](https://cloud.githubusercontent.com/assets/485600/3760773/2e5e3b52-187e-11e4-9e80-ac53eba703b3.png)

Button reads "Dokumente extrahieren", should be "Anhänge speichern". Also, description should use wording "gespeichert" instead of "extrahiert".

Furthermore, caption title "Anhänge" should be something like "Zu speichernde Anhänge".

Typ column is empty (for pdf content).