This patch integrate the scout widgets with Genode's new API headers
'util/geometry.h', 'os/surface.h' and 'os/texture.h'. Thereby, we get
almost rid of the platform-abstraction shim that was never used anyway.
Furthermore, it extracts the parts that are worth reusing from the
scout implementation to the public location 'demo/include/scout'.
This patch enables the recursive startup of launchpad instances, which
was not possible since the recent removal of launchpad's built-in
default configuration.
This patch updates the launchpad config to use XML attributes and
removes the built-in default configuration (which is only meaningful
for demo.run anyway).
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.
