Fixed some problems with synchronization between the attachments in

Fixed some problems with synchronization between the attachments in
the attachments view of the editor, and the internal attachments list
the editor contains (fixes NB#57756):
* src/widgets/modest-attachments-view.[ch]:
        * Added the method modest_attachments_view_get_attachments, that
          obtains the mime parts of all the attachments shown.
* src/maemo/modest-msg-edit-window.c:
        * Now, set_msg updates the list of attachments from the
          attachments view.
        * Fixed the code to hide and show the attachments caption.

pmo-trunk-r2095