Without limiting the size of the launchpad window, the application
prepares itself for the worst case, taking the screen size as maximum
size to allocate its pixel buffers. Limiting the maximum width to a
reasonable value reduces the memory footprint.
As a preliminary step for working on issue #11, this patch revisits the
'Framebuffer::info' RPC call. Instead of using C-style out paramters,
the new 'mode()' RPC call returns the mode information as an object of
type 'Mode'. Consequently, mode-specific functions such as
'bytes_per_pixel' have been moved to the new 'Framebuffer::Mode' class.
