Usability improvement: provide feedback

[RinzeVanDerBrug]

If you don't check any box and try to perform an action, nothing wil happen. The actions won't be clickable. It'll be impossible to perform an action, but no feedback is provided. In the context of usability, it would be nice to provide a message like: 'Please select a resource to perform the action on first!'. This would especially improve first-time user experiences.