Support for resizing windows on all sides
Finished full window resize support

- The main run loop resets the cursor if it falls outside of all windows during a mouse move.
- Added cursors supported by CSS that are not in NSCursor.
- Code cleanup in CPCursor.
- Cursors now indicate available resize directions if there is a window min/max size.
- Reduced slop to 3, what it is in Cocoa.
- Added a second non-min/max window to the demo.
Constrain window resize to usable area of platform window.
Optimisation.
Window resize fixes

- Track mouse exit from window resize rect instead of unconditionally setting arrow cursor.
- Don't show the resize cursors for full platform windows.
- Show the resize down cursor if the top of a window is being resized and it has reached the bottom of the menubar.
- Make windows in CPToolbarTest resizable to test resizing behavior with toolbars.
- Added a full platform window and menubar to the test app.
Merge pull request #1711 from slevenbits/new-window-resize

This commit provides resizing of windows from all sides. The legacy style, which displays a resize thumb in the lower right, can be restored with [CPWindow setGlobalResizeStyle:CPWindowResizeStyleLegacy].