Completing the document-based app setup.

Multiple repositories can now be opened by using the File → Open… menu option.
Each document is a PBGitRepository with a PBDetailController controlling the window. PBRepositoryDocumentController is the document controller.
When launched, the application will attempt to open a repository with the current directory as its path. If this fails it will display an open panel to allow the user to select one.

PBRepositoryDocumentController.h

@@ -0,0 +1,17 @@
+//
+//  PBRepositoryDocumentController.h
+//  GitX
+//
+//  Created by Ciarán Walsh on 15/08/2008.
+//  Copyright 2008 __MyCompanyName__. All rights reserved.
+//
+
+#import <Cocoa/Cocoa.h>
+
+
+@interface PBRepositoryDocumentController : NSDocumentController
+{
+
+}
+
+@end