IDN is not installed on all machines making the unit test execution fail on those without. Let's make IDN thus a pre-requirement for the text execution.
Replaces the OC_Mail and phpmailer with SwiftMail allowing us to mock it properly.
Fixes the unit test execution on master on local machines and https://github.com/owncloud/core/issues/12014
Conflicts:
3rdparty
lib/private/server.php
lib/public/iservercontainer.php
tests/lib/mail.php
tests/settings/controller/mailsettingscontrollertest.php
Conflicts:
3rdparty
lib/private/mail.php
lib/private/server.php
lib/public/iservercontainer.php
settings/ajax/lostpassword.php
settings/application.php
