Use allowMultipleFiles
Remove redundant init method.
Implement GuiCocoaScrolledWindow
Implement GuiCocoaScrollBar
setUserData
Add modified mask and key equivalent
Remove log
Setup resizing mask so views favor the top of the window. Set document view for  GuiCocoaScrolledWindow.
Implement GuiCocoaCheckButton
Add GuiCocoaScrolledWindow and GuiCocoaScrollBar
Set up CGContextRef for Cocoa
Handle drawing, mouse and key events.