Make Ctrl+s save workspace, not take a screenshot by default

[hdo]

Ctrl+s saves the open document in any other app. I think it makes a lot have sense to have Bookmap save the workspace instead of taking a screenshot. In particular as "save workspace as" has the matching Ctrl+Shift+s shortcut. I know shortcuts can be changed, still I think it's a really strange default. I've probably taken a gazillion of unintended screenshots before finally changing the shortcut to save workspace.