Don't send messages content in e-mail notifications

I've added it here

https://mattermost.uservoice.com/forums/306457-general/suggestions/15425175-don-t-send-message-contents-in-email-notifications

I hope you all will upvote for it. As I've said, this is a problematic potential leak for our organization. One of the reasons MM is a good solution for us is that we would control its data. Sending these types of notices out via email potentially circumnavigates that control.

Thanks, I hope this can be addressed.

Thank you!