Video rooms copy tweaks

[nadonomy]

@robintown issue as promised! From dogfooding, copy tweaks to make:

• Relabel 'Video room' to 'New video room' in room list context menu
• Relabel 'Connect now' to 'Join' in main lobby state
• Relabel 'n people connected' to 'n people joined' in lobby state
• Relabel 'Connected' to 'Joined' in room list

cc @gaelledel to track this when you're back!