wizard: fix the photo edit

On some devices, the application crashed when we changed the photo in
the account wizard because the Bitmap was too big to be saved.
Now, we save the photo as byte array instead of Bitmap to prevent it.

Tuleap: #1543
Change-Id: I715f799d64c0a527586937f3da2f5d9b590347b3
Reviewed-by: Alexandre Lision <alexandre.lision@savoirfairelinux.com>