Allow to connect to servers with self-signed TLS certificates

[HenkKalkwater]

Some users use self-signed TLS certificates, which Sailfin simply rejects at the moment.

I'm thinking of implementing it in the following way:

Functional requirements:

• When a TLS error occurs, prompt to user on what to do.
• Sailfin should remember the user's choice to ignore TLS errors which can be ignored.
• For errors about self-signed certificates, Sailfin should ask the user on which certificate to trust and remember it, but it should not automatically trust all self-signed certificates.

Implementation steps

• Listen for the QNetworkAccessManager::sslErrors signal and display them properly in the user interface, allowing users to ignore them.
• Set the QNetworkAccessManagerFactory on the QQmlEngineInstance to create a QNetworkAccessManagers for the QML side to use, so that the QML part respects the user's choice to ignore TLS warnings as well.
• Let the media player (gstreamer) respect the ignored TLS errors
• Store the TLS errors that the user has ignored and retrieve them later.