libappfw: Added Untrapper for mouse untrapping convenience
Refactor|libappfw|Client: Use Untrapper in dialogs and tutorial
UI|Client: Order of key modifiers in pretty-printed binding
Refactor|libdeng2: Moved convenience getters from Config to Record

These get*() methods are useful with any Record, not just Config.
Tutorial|Client: Adjusted highlight flash

Less distracting while being noticeable.
Tutorial|Client: Automatically show tutorial if not shown before

Config.tutorial.shown determines whether to show the tutorial at
startup.