10.7 full screen support

Add several methods in WLMainFrameController class to handle 10.7 style
full screen mode. The toolbar and tabcontrol are hidden in fullscreen
mode. But there are still empty strips on top and bottom of the screen.
Hide strips on top & bottom of the screen when entering full screen mode.
Clear the codes
Validate fullscreen related menu items

Entering/Exiting fullscreen (old Welly style) menu item will be
disabled in 10.7 fullscreen mode. Increase/Decrease font size menu
items will be disable in 10.7 fullscreen mode & old Welly style full
screen mode.
Rename old Welly style fullscreen mode to "Presentation Mode"

Now both 10.7 style full screen mode and old style presentation mode
can concurrently exist in menus
Toggle menu text for toggle presentation mode
Disable Toggle Full Screen button and menu item when in presentation mode
Exit Full Screen Mode before closing Welly
fix the opaque property of main window after exiting full screen mode
Fix the top/bottom strips when entering full screen mode
Deal the case when ratioH < ratioW

Besides, change the setFont: method. Now the original size parameters
are stored when entering fullscreen/presentation, and restored when
exiting. This should prevent ruining shape by repeating enter/exit
fullscreen.
2.7 alpha version launched