Allow organizer to change which tab is the default when people load the meeting

[timbl]

Having the metadata table for the meeting as the default is often not what you want. Specifically, if there is a chat that should typically be the default tab. If there is unfinished poll, that should take precedence by default, but the users should always be able to change it.

Could - change the default; could - change the order and always make the first one the default.