make sure to enable incognito mode when mounting a public link and update init status of the encryption app

movie previews: use file directly when it's stored locally and encryption is not enabled

fix mail settings save function - ref #8854

Refactor OC_DB::connect() to properly support sockets.

move mail template settings to templateeditor repo

fix some minor issues

Added max heartbeat interval to prevent integer overflow 

When using big session timeout values, the interval value might
overflow and cause the setInterval() call to ping the server in a loop
without any delay.

This fix adds a maximum ping interval of 24 hours.

Forward port of 00ec5fc1935c946e846a8ff28491e5b5b017b3d7 from stable6.