Support setting an email address as preferred email address via REST

It is now possible to set an email address as preferred email address
for an account by PUT on
/accounts/<account-id>/emails/<email-id>/preferred.

Change-Id: I4dcc393174bfa04cca4e4a240d98c89e3b3cc6bb
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>
3 files changed