Make some annotations not clickable

[ceesem]

I generally leave the bounding box annotations in the image and segmentations on because they are the only global spatial reference available. However, when using right click in the 3d view to go to specific locations, these bounding box annotations can capture the cursor and the user is transported far away from the desired location. In other cases, it is handy to have a guide to certain locations (for example, a layer boundary or nucleus points) while wanting to use clicking to target something else (meshes only, for example). In general, a toggle in each layer that allowed one to set the clickability of annotations would be extremely useful, so one could have full flexibility of what objects should capture the cursor input on the 3d view.