Bug 7780: make silent/verbose flag for translation installing

Bug 7780: make silent/verbose flag for translation installing

This patch deal with the -v flag that you can put on translate script.
If you run without -v, the process should be silent
if you run with -v, the process should be verbose

Signed-off-by: Frédéric Demians <f.demians@tamil.fr>
I've refactored your patch to handle verbosity directly via a translator
attribute, rather than with parameter which has to be send to each object call
method.

Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>