Added Shift+Enter shortcut to search backwards

https://bugzilla.gnome.org/show_bug.cgi?id=641797
ev-utils: improve Save Image As dialog

This commit makes the dialog more like the 'Open...' dialog.
The 'By Extension' filter is changed to an 'Supported Image Files' filter with all the
supported mime types added. An 'All Files' filter is added as well.

And to make it more like other dialogs, the supported formats are added with
just the description as name.

https://bugzilla.gnome.org/show_bug.cgi?id=523071
Show file uri in error message when it fails to open

https://bugzilla.gnome.org/show_bug.cgi?id=697900
djvu: add support for file identifiers

https://bugzilla.gnome.org/show_bug.cgi?id=619410
Updated Spanish translation