-Added 'g' shortcut key that will act as the Gameshark button.
-Added user ability to map a joystick button to the Gameshark button.
Note, I did not add support for the Gameshark button to the emulator core yet, so cheats triggered by the GS button will not work until that's done.
-Added new tab to configuration dialog for user to create mappings.
-Minor fix: Reset configuration dialog to have first tab selected everytime it's shown.