Add an option to exclude invisible objects from floorplan generation

[misslivirose]

Issue:
With the current behavior in Spoke, geometry that is marked as 'walkable' is included in the calculation for generating the floor plan. However, this can sometimes be undesirable behavior, since it complicates the floor plan and creators may not intentionally be including invisible meshes.

Proposed solution:
We should introduce a checkbox on the floorplan generation panel that says something like 'Include invisible meshes in floorplan'. This would decide whether or not invisible elements should be part of the calculation.

Our open question is whether or not we should change the default behavior. If we keep the default behavior the same, the check box would exclude invisible meshes. If we change the default behavior to exclude invisible meshes, the check box would be to include the invisible meshes. In the event that we change the default behavior, we might want to consider signaling that in some way so that we can let users know that the floorplan generation behavior has changed.

[brianpeiris]

Another suggestion to avoid changing the default: Have an option or command to recursively toggle a subtree in the hierarchy as "walkable", or not.

[cvanmeurs]

I'd also add that I'd like the same to be done for collision (so that objects that are turned off are not calculated to generate the collision).

[robertlong]

I think I've solved this with #1079

Let me know if that covers everything here.