Allow to isolate root elements without altering the tree collapse state

[njourdane]

Isolating an element with shift+click also expands the element tree.

It could be practical to isolate root elements without altering the tree collapsing state (which node is collapsed and which is expanded). This way we could easily navigate between root elements.

ux proposal:

• keybord: page up / page down to isolate previous / next root element;
• ctrl + click on the element in the tree.

For a better understanding of my use case, I'm working on bd_shape_history, which is a tool to visualize the modification history of Build123D objects, so we can display a visual diff between each step:

Being able to quickly navigate between each "step" (which are just regular objects) would be very handy in this case.