Devel reverts recent UI work

[Edward K. Ream]

Rev 74bf72e (PR #3217) in devel reverts PR #3214.

I don't know for sure what caused a recent hard crash, but PR #3214 is a likely culprit. Leo's tree code is notoriously fragile.

Imo, I have no choice but to revert the recent code.

Edward

[Thomas Passin]

I don't think it's the new code, as I said on the other thread.  I think there are some Qt problems in general, but I don't think they are from this.   I've submitted a new PR that has a setting that needs to be set to True to enable the new behavior.

The code did require something new, and I suppose it's possible that it matters.  To get the ItemEntered event to be emitted, "mouse tracking" has to be turned on for the tree.  By default Qt has this disabled.  I don't know why it would matter, but presumably there would be more mouse events generated than there used to be.