Fix activation for render/molecule tree view widgets
Fix activation for render/molecule tree view widgets

Mac evidently does not send activate() signal after clicking.
Now clicking on a row will properly activate.

ghutchis/avogadroapp,ghutchis/avogadroapp,ghutchis/avogadroapp,OpenChemistry/avogadroapp,OpenChemistry/avogadroapp,OpenChemistry/avogadroapp,ghutchis/avogadroapp,OpenChemistry/avogadroapp