Make the message dialogs more modern

Make it a real GtkMessageDialog.

Also, remove the icon, we not needs it anymore.

https://bugzilla.gnome.org/show_bug.cgi?id=735438
Make the error dialogs more modern

Make it a real GtkMessageDialog.

Also, remove the icon, we not needs it anymore.

https://bugzilla.gnome.org/show_bug.cgi?id=735438
request-dialog: Remove the unneeded image

https://bugzilla.gnome.org/show_bug.cgi?id=735438
file-selector-dialog: Use symbolic icon for the go up button

https://bugzilla.gnome.org/show_bug.cgi?id=735438
updated version number