New: added methods to globally turn off window constraining when resizing the platform window.

Previously, whenever the platform window (virtual screen) resized, windows were moved or resized to keep them on screen. This could not be easily overridden by the user.

Two class methods have been added:

CPWindow +setConstrainWindowsToUsableScreen:
CPWindow +constrainWindowsToUsableScreen

If +setConstrainWindowsToUsableScreen:NO is called, then resizing the platform window will not move or resize user windows.
Fixed: resizing a window did not attempt to maintain a minimum margin on screen.

Previously, window moves were constrained such that a minimum margin of the window was visible on screen, but window resizes were not constrained, allowing the user to effectively move the window off screen.

Now resizes are constrained such that a minimum margin of the window is always visible on screen so that the window does not get "lost".
Docs
New: moved application constants to a separate file.
New: notify when the platform window resizes.

The platform window is the virtual screen for Cappuccino windows. Per Cocoa, when the screen (platform window) resizes, CPApplicationDidChangeScreenParametersNotification is sent and the CPApplication delegate method applicationDidChangeScreenParameters: is called.
Fixed: window width was not constrained when platform window was resized.

Previously window heights were constrained to the usable screen when the platform window (virtual screen) resized, but widths were not. The code was there to constrain the width, but it wasn't being used.

This commit ensures the width constraining code is executed.
Formatting, optimizations.
New: sort the keys in CPDictionary -description.

This makes it easier to find an item in a large dictionary.
Fixed: constraining window's to the screen did not respect a window's minSize.

Previously, when the platform window was resized, windows were moved/resized to stay within the virtual screen, but if the window had a minimum size, it was not respected.

This commit ensures that if a window has a minimum size, it will always be respected.
Fixed: when constraining a window resize, the horizontal margin was fixed (and too large).

Previously a fixed margin of 40px was maintained at the left/right of a window when resizing it, which was excessive.

Now the minimum size allowed during a resize is the same as the minimum margin allowed when moving a window, which is determined based on the type of window.