[Cocoa]Windowflags are handled incorrectly for all window Types

Windowflags are only handled correctly for some of the on OSX supported combinations.

In QT::Window, QT::Dialog and QT::Tool it is impossible to disable the maximize buttons other than hiding the frame.

QT::Dialog and QT::Tool should without QT:CustomizeWindowHint only have the close button enabled.
QT::Window should have Close, Minimize and Maximize enabled.

It is possible to enable and disable all buttons separately and Osx will hide them if Close, Minimize and Maximize are all disabled.
This can desirable for modal dialogs as stated in the Human interface guidelines ( https://developer.apple.com/library/mac/#documentation/UserExperience/Conceptual/AppleHIGuidelines/Windows/Windows.html ).

I attached a patch that in my oppinion fixes the behavior for most of the window types.