Just discovered a way to keep quicklook windows open when working in applications other than finder. Its quite helpful!
In terminal:
defaults write com.apple.finder QLHidePanelOnDeactivate 0
Then relaunch finder (option+R Click on Finder --> Relaunch)
In terminal:
defaults write com.apple.finder QLHidePanelOnDeactivate 0
Then relaunch finder (option+R Click on Finder --> Relaunch)