Include discard option in save dialog when closing

When closing an unsaved analysis, the user sees a dialogue asking to save the analysis with the two options “cancel” (=don’t save and close) and “save” (=well, save). Similar to many desktop software, it would be helpful to expand this to

“cancel” (=don’t save and don’t close)
“discard” (=discard changes and close)
“save” (=save and close)

so that the user can have a look at the analysis to see if they want to keep the changes (especially helpfull when you’re closing the analyses while you’re e.g. in the filebrowser and use the analysis designer drop down menu to close the analyses).

(from redmine: issue id 1072, created on 2012-07-11 by root, closed on 2012-10-18)