Clean up what items are checked/unchecked

[sabinachND]

Rules (feel free to ask Sabina to clarify):

• When a top layer is checked, then all nested items should be checked.
• When a top layer is unchecked, then all nested items should be unchecked.
• When all nested items are checked, then top layer should be checked.
• When all nested items are unchecked, then top layer should be unchecked.
• When some nested items are checked or unchecked, then the top layer should show a dot.

Note that this fix should apply to all elements in the sidebar of potreeND, not just the sensor readings.