GTK client uses D-Bus, so is unable to forward exceptions.
This causes crashes of daemon (unhandled exception).

This patch changes DataTransfer API to not throw (noexcept).
This is an important changes, not backware compatible,
so the API version has been modified consequently.

Change-Id: I9f2a2fe1732b2622ace16225b6e792dc15383ba1
Reviewed-by: Anthony Léonard <anthony.leonard@savoirfairelinux.com>