testing bugfix: prevent the raise of ServerConfigurationError if the email_settings.ini file is missing
and we are in TESTING mode.

A TESTING constant is dynamically defined using <__name__> module attribute
and used to set the testing mode. If we are in testing mode,
the email_settings.ini file is ignored.
useless repeated code removed: no more need to set app.config['TESTING'] to True from test_server.py,
since the parent commit.
'email_settings.ini.example' file with empty values added to the repo.
This should close the issue #22.