Display trust as a tree

[jw3]

Another take on the trust view would be to make it a tree, rather than a list of fully qualified paths.

This would allow the model to be populated while the view remains unchanged unless action is taken. Even if action is taken, it will be a fraction of what happens in the list view.

The tree nodes still be inserted piecemeal as the async events are coming in, but they remain in collapsed state until clicked.

This would eliminate #520

This should also help greatly with #738