Implemented "middle click on selection" behavior, to signal when to recompute histogram data.
Implemented "middle click on selection" behavior, to signal when to recompute histogram data.

aashish24/tangelo,mathstuf/tangelo,aashish24/tangelo,ecohealthalliance/tangelo,ecohealthalliance/tangelo,Kitware/tangelo,Kitware/tangelo,ecohealthalliance/tangelo,mathstuf/tangelo,aashish24/tangelo,Kitware/tangelo,mathstuf/tangelo