Disable 'Track sent emails' setting for all channels

Our "seen" tracker tell users when an email has been read by the recipient. It can be disabled for a given channel if it is regarded as too intrusive, however, this is not scalable if an admin wants to ensure it is disabled across all channels.

We could introduce a new company setting to disable the "Track sent emails" across all channels, which cannot be overridden for a user's individual channels.