Joining a meeting should perhaps close the joiner's current models

[tomgoddard]

When joining a meeting the currently open models in the joining LookSee are sent to the other participants. This behavior is maybe not the best, and it may be better to close any models in the joining LookSee and just receive the current meeting models. With the current behavior if a participant leaves the meeting, their headset still shows the meeting models, and if they rejoin then those models will be added to the meeting and there are then 2 copies of every model in the meeting, not good.