Applications previously had to create a GUI::Menubar object, add menus
to it, and then call GUI::Window::set_menubar().
This patch introduces GUI::Window::add_menu() which creates the menubar
automatically and adds items to it. Application code becomes slightly
simpler as a result. :^)
ImageViewer used two different logic to resize the display window, which
leads to confusing behaviour for rotate function. Now all the resizing
behaviour goes through the existing resize_window function.
ImageViewer window kept growing while zooming in, which causes out of
memory error and crashes the application. Now, only the image content
is rescaled and the window size is preserved.
We also open the display window as the same size as the image, which may
cause a similar issue for very large image files. This is prevented by
limiting the maximum window size to be the screen size.
This changes (context) menus across the system to conform to titlecase
capitalization and to not underline the same character twice (for
accessing actions with Alt).
Previously some actions like Rotate/Flip/Set as Desktop Wallpaper would
make the application crash if no image was loaded. Now image actions are
enabled/disabled based on whether an image has been loaded or not.
