Ubuntu: Smtp settings

Implemented SmtpManager class to store smtp settings

SmtpSettings page.qml only shows relevant input fields for each MSA Connection method

Default ports are tested and removed knowlege of default ports in QML. A warning
is shown if ports are not the default for the connection method

REVIEW: 117588

Change OutgoingPage of the desktop settings dialog to use SmtpAccountManager

Also changing the UI to choose submission type via Method and Encryption combo box's

jkt: Changed to only use a single enum for submissions because that's,
unfortunately, a pretty big QML limitation. Having this enum embedded within a
QObject is the lesser of two evils, IMHO.

jkt: Some refactoring

jkt: Fix handling of state changes whenb toggling the checkboxes and its
interaction with the configuration backend

jkt: Fix label hiding and the default index of the encryption combobox when
switching methods