Update selection logic for qtModelEntityItem
This MR changes the selection logic for qtModelEntityItem such that when user is selecting model entities in operator, it would highlight the entity that mouse is hovering over and added the selected cells into qtSelecionManger which would update realtime in render window and model tree.
Check SMTK commit 20db928697be609da8a14817dd99b9dc35afe2e0 for detail.
Merge !472 first.