Add sendemail.from to control setting From header

Configuring sendemail.from enables the site administrator to control
how Gerrit will setup the outing email's From header in the message
envelope.  Some sites may prefer using a single address that Gerrit
sends from, while others may prefer forging the user's own email if
they are all on the same domain.

Change-Id: Ie19c4a3c50cc92f39af6fe6b43ba8aabb37b5077
Signed-off-by: Shawn O. Pearce <sop@google.com>
11 files changed