Show proper error message if registering email address fails

Users can register new email address under 'Settings > Contact
Information'. If the registration fails, e.g. because the mail server
is incorrectly configured or because the mail server refuses to send
the email, an error dialog with 'Code Review - Error > Server Error >
[message]' is displayed which makes the user think that there is
something wrong with Gerrit. Slightly improve the error reporting by
setting a proper title for the error dialog and removing 'Server Error'
from the message.

Bug: issue 1480
Change-Id: I788e5bdf69aaaee17a1fd468f81d3effaa13a624
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>
27 files changed