Add a toolbar icon for the HUD window, which required making DebuggerController the...

Add a toolbar icon for the HUD window, which required making DebuggerController the action handler.

* Icons/HUDIcon.png: New icon
* CONTRIBUTORS: Add credits for icon
* MacGDBp.xcodeproj/project.pbxproj: Project updates for icon
* Source/AppDelegate.h+m:
(showInspectorWindow:): Moved to...
* Source/DebuggerController.h+m:
(showInspectorWindow:): new from ^
* English.lproj/Debugger.xib: Add toolbar item
* English.lproj/MainMenu.xib: Change Window-->Inspector's target